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Basic Guides

Welcome To Our Basic Guides Pages

On this collection of pages, we hope to give you the basic information you need to make the right choices when purchasing the equipment to set up your aquarium or pond.

Where we have used pictures to illustrate certain types of equipment, please remember that this is not an endorsement of that particular manufacturer's product.


Why do you need a Filter?

It is possible to maintain an aquarium without any filtration at all (natural bio-system) by having few fish in a relatively large quantity of water, and lots of plants. However, most of us would not be content with just a few fish in a large tank, and having lots of plants may not be possible with certain species of fish. Therefore, some method of filtration is necessary to maintain the water quality. We will now go on to discuss the various types of filtration available to the hobbyist.

Air-Driven Sponge Filters

A very basic, cheap, but very effective filter, consisting of an uplift tube with one or more sponges attached at the bottom. Requires an air supply (aquarium air pump) to operate it. Only really suitable for small tanks up to 61cms (24 ins). The sponges should only be cleaned out gently in old aquarium water during water changes, as beneficial bacteria living in the sponge material would be destroyed in chlorinated cold tap water. A very useful filter for breeding tanks as the fry will not be sucked into the filter.

Air-Driven Internal Box Filters

Usually square, clear plastic containers which sit on the floor of the aquarium, which require an air supply (aquarium air pump) to operate them. The container is usually packed with filter wool, but other filter mediums such as carbon can be used. Cheap but effective, if perhaps a little unsightly within the aquarium. Single units only suitable for tanks up to 71 cms (30 ins), but more units could be used for larger tanks.

Undergravel Filters

This consists of a plastic plate (or more than one inter-locking plates) which is positioned inside the aquarium on the glass base, and covered with about 2 ins of gravel. One or more uplift tubes (depending on the tank size) are connected to the plate generally in the tank corners where they are not so conspicuous. The uplifts are either air operated or fitted with powerheads, which draw the tank water down through the gravel, along under the plate, and up the uplift tubes and return it to the aquarium. The gravel bed, being fed with oxygenated water containing nitrites (produced by food and fish waste) becomes colonized with a vast number of beneficial bacteria, which break down the nitrites into much less harmful nitrates. Undergravel filters are very efficient biologically, but the solid waste which collects within the gravel should be removed occasionally using a gravel cleaner when carrying out a partial water change. A very popular method of aquarium filtration.

Electric Internal Power Filters

Produced by a wide variety of manufacturers, electric internal filters are very easy to use - place it in the tank, plug in and switch on. There are sizes to suit all aquariums up to 120 cms (48 ins), beyond that, more than one unit would be required. A big advantage is the lack of noise produced when running. All electric internal filters use a sponge as the main filter medium, which should be cleaned out occasionally in old tank water whilst doing a partial water change. In addition to the sponge, some makes of filters have facilities for adding carbon, whilst others can be fitted with a carbon sleeve instead of the sponge. Another facility available on most internal filters is the ability to suck air from above the water, and vent it with the filter output water, thus producing extra aeration.

Electric External Power Filters

These are canister type filters which would be positioned outside of the aquarium below the tank water level, as a syphon effect is required for the water to be fed to the filter. The filter is connected to the aquarium by two flexible plastic tubes, one supplying tank water to the filter, the other returning the filtered water back to the tank through either a jet pipe or spray bar. These are the most expensive types of filter, and are generally used for larger tanks. The great advantages are the increased flow rates, and the fact that different filter mediums (including sponge, ceramic tubes, carbon, ammonia removers, filter wool, peat etc) can be used in the containers which are fitted in the canister.

Fluid Filters

A relatively new idea for biological filtration. A canister filled with aquarium water is position on the outside of the tank, and contains a quantity of special sand. A pump or powerhead is required to pump the aquarium water in at the bottom of the canister, and out and back to the aquarium from the top. This causes the sand within the canister to be constantly in suspension, thereby allowing a far greater build up of beneficial bacteria on and in the sand particles than could ever be achieved with a normal undergravel filter bed. The flow rate of the water through the canister is critical and has to be adjusted to ensure the sand stays in suspension, but does not reach the top and end up being deposited back into the aquarium. The fluid canister filters are expensive, and added to that is the cost of the pump or powerhead. These filters are generally used by hobbyists keeping tropical marine tanks.

Eheim Wet and Dry Filters Guide

Modus Operandi

The float is the only mechanism which changes the water flow from the spray bar. The pump motor runs at Full Speed : ALL THE TIME.

When newly installed the filter will fill in about one minute or less. Check this time and make a note : as time goes by and filter starts to get clogged with detritus, this time will increase. When filling time reaches 3-4 minutes then cleaning should be carried out.

Filter Positioning

The filter should be positioned below the aquarium. The distance between the aquarium water surface and the bottom of the filter must be within 100 - 120cm. This installation height is absolutely vital to guarantee the correct rhythmic functioning of the wet & dry filter

Feed and Return Hoses

Ensure that the two hoses are same length (cut to adjust if necessary) and they are laid out smoothly with no kinks. During use it is also important to regularly check the hoses for furring up. Any restrictions here can affect the functioning of the wet & dry cycle.

Breather Hose

The breather hose must be positioned in the tank with the outlet un-obstructed and clear of the water's surface. Ensure outlet end of breather pipe is not sitting on any aquarium stress support strips. If the outlet is restricted in any way the wet & dry cycle will be affected.

Hose Fittings Supplied

If the filter flow rate is altered by the addition of valves, taps etc, or extra holes drilled in spray bar, the wet & dry cycle is likely to be affected.

Filter Media

Use of incorrect filter media, extra fine foams or filter wool, or the correct filter media packed too tightly or if it is clogged with detritus : all these will affect the wet & dry cycle.

Loud Gurgling Sound from Breather Hose

As the filter refills with water, the air in the canister is exhausted via the breather hose. If the top area of the filter floods due to partly clogged media, water can be carried up the breather hose by the force of the exhausting air, causing a loud noise.

Check installation height : if above 120cm the water flow into the canister is so powerful that the top area of the filter floods. Partly closing the intake tap when gurgling is heard should overcome this problem in the short term. Filling time should be adjusted to approx 30 seconds.

Filter will not fill with water

The pump empties the filter - the float drops - but filter will not refill. Usually a sign of clogged hoses or media. The pump is pumping the water out as fast as its coming in. The water should always flow into the filter continuously : it does not slow down at any time during the wet & dry cycle. So if the filter does not fill, the water supply is restricted.

Float is Up : Filter will not Empty

Pump may also be very noisy. Possible that solid rod has dropped out of the ring under the impeller. This allows air from the breather hose to mix with water in the impeller causing the noise. Refit the rigid rod into the ring under the impeller. Also check that the cleaning plug is in place in the pump head.

Effects of Modifications

Replacing Spray Bar with Diffuser : likely to cause increase of back pressure on outlet hose, which produces a reduced suction to the float which allows it to rise with only 2 inches of water in the filter.

Reducing curve on shepherds crook inlet pipe : causing a kink in pipe and reducing flow by up to 70% : so float rises with only 1 inch of water in the filter.


Why do I need a heater?

Tropical fishes need to have their aquarium water maintained at it's natural temperature. For most species, 75░ F (24░ C) is suitable, although some specific species are happier at higher temperatures. Coldwater fishes such as Goldfish do not usually require extra heating, although the fancy coldwater fish such as Fantails, Orandas, Lionheads etc seem to do much better at almost tropical temperatures. It follows therefore, that in areas where the ambient temperature is lower than that quoted above, some method of raising the water temperature is required.

Combined Heater/Thermostats

The use of a combined heater/thermostat is the most popular method of heating an aquarium. It consists of a sealed glass tube, within which is contained the heating element, and above that is the thermostatic control. The glass tubes are now permanently sealed to prevent access to the electrics by the consumer; any adjustment to the temperature setting being carried out by turning the external adjustment.

What Size Heater do I Need?

The wattage of heater necessary to maintain the required aquarium temperature depends on a number of factors:

  • The volume of water to be heated
  • The temperature to be maintained
  • Room temperature variations
  • The dimensions and level of insulation of the aquarium

Where do I place the Heater?

The unit should be placed at the bottom of the aquarium to encourage even heating throughout the tank. The heater should be positioned either horizontally or at a 45░ angle with the thermostat above the heater, using the clips and suckers provided. Do not place the suction holder over the heating element. It is essential that no part of the heater is either in contact with the glass or any other material in the aquarium. DO NOT BURY THE UNIT IN THE SAND OR GRAVEL, as this would result in the cracking of the heater glass. The heater must be submerged at least to the minimum water level marked on the glass tube at all times.

How Do I Adjust the Temperature Setting?

Disconnect the heater from the mains. Wait 15 minutes for the heater to cool, before removing it from the water. Less expensive units only have an adjusting knob, with no temperature setting scale, so these should be altered by turning the knob no more than a quarter-turn in the direction needed as indicated on the heater. Replace the heater in the aquarium, switch on, and leave to settle for 12 hours, monitoring the temperature carefully until it has settled down. Re-adjust if desired temperature is still not achieved. More expensive heaters have a temperature setting indicator as well as the adjustment knob, so these are easier to re-set. Turn the adjusting knob until the desired temperature is indicated, replace in the aquarium, switch on and monitor the temperature carefully until it has settled down. Re-adjust if necessary.

Cautions :

  • Always disconnect from the electricity supply when the unit is out of the water or before putting your hands in the water.
  • Always disconnect from the electricity supply when the unit is out of the water or before putting your hands in the water.
  • Always let the heater cool down for 15 minutes before taking it out of the water.
  • Always leave 24 hours for temperatures to stabilize before introducing fish.
  • These units are not intended to be used in bathrooms.
  • The supply cord of heater/thermostats cannot be replaced. If the cord is damaged, the heater should be discarded.
  • The water level must be kept at or above the minimum water level indicator line.
Selecting The Right Size Heater
Watts Length Volume
cm gallons litres
50 18 46 5-10 23-45
100 24 61 10-20 45-90
150 30 76 15-30 68-135
200 36 91 20-40 90-180
250 48 122 30-60 135-270
If the aquarium is in a cold location, or a temperature of over 26° C is required, select the next highest wattage for your size of aquarium.
(Information courtesy of Interpet Ltd)

Fluval E-Series Aquarium Heaters

The Fluval E-Series Aquarium Heaters may need to be reset, to do this turn off the heater and re-position the heater on a 45 degree angle. Then turn on the heater and turn the temperature down as low as it will go (18 degrees), then turn the temperature up as high as it will go (34 degrees). After this set the heater at the desired temp and leave the heater at a 45 degree angle.

There are no problems with the heaters, the only issue is that the heaters need to be positioned on a 45 degree angle to disperse the heat. The heaters are so sensitive, they will read the water temp inside the heater guard if positioned vertically.

Fish Health

(Information courtesy of Interpet Ltd)

Three Golden Rules for Healthy Fish

  1. Provide good aquarium conditions
  2. Exercise constant vigilance
  3. Accurately diagnose and treat disease

What Causes Fish Disease?

There exist many lower life forms such as virus, bacteria, fungus, protozoan and other parasites, some of which can only survive by living in or on fish. Not all of these are undesirable, although some have the potential to cause disease to their fish host and are called pathogens.

Where Does Fish Disease Come From?

  • Every aquarium naturally contains pathogenic bacteria and fungus spores as part of its normal flora and fauna.
  • Every fish also carries its own population of parasites and bacteria, some even carrying internal fungus.

With all these disease organisms naturally present it may seem surprising that fish are not constantly suffering from disease.

How Do Fish Remain Healthy?

Healthy fish like other animals have their own very effective system for fighting naturally present disease organisms called their immune system. This system creates barriers which initially prevent the disease organisms from attacking the fish. Should any disease organisms manage to breach this barrier, the immune system also has agents which actively attack the disease.

So, in a healthy aquarium the fishes' natural immune system efficiently keeps the pathogens at bay. However, there is a delicate balance that must be maintained between the fish and the disease organisms for the fish to remain healthy and disease free.

What Happens if the Balance is Upset?

If the balance between the fish and the disease organisms present in the aquarium is upset, a disease outbreak will occur. There are three ways in which this balance can be tipped:

  • By the fish becoming stressed. This reduces the effectiveness of the immune system.
  • By the population of pathogens rapidly increasing as a result of condusive conditions.
  • New disease organisms being introduced into the aquarium.

How Can Fish Disease be Prevented?

The likelihood of a disease outbreak occurring can be reduced by following these simple rules:

  • Feed a good, varied, balanced diet. A staple flake diet supplemented with frozen or freeze dried food for variety.
  • Maintain stable water quality which matches the needs of your fish. Water quality should be monitored regularly with simple to use and accurate test kits.
  • Carry out regular water changes to maintain water quality. Remember to use a water conditioner to make tap water suitable for aquarium use.
  • Use appropriate aquarium decoration, allowing sufficient hiding places and providing for any special needs of individual fish species.
  • Ensure all aquarium inhabitants are compatible. If in doubt, take the advice from your local aquatic retailer.
  • Add aquarium salt (1 gm per litre) to reduce stress in freshwater fish.
  • Maintain water clarity using aquarium treatments (such as Interpet's Filter Aid and Green Away) in combination with a good filtration system.

These steps should form a basic programme for the care of your aquarium. However, particular situations can still tip the balance and cause disease outbreaks.

Fish Stress Stress is the main cause of fish disease. Stress is caused by a number of factors, e.g. poor water quality, bullying by other fish, capture or movement of the fish, insufficient hiding places, poor nutrition. When fish are stressed their immune system breaks down allowing disease to attack.

Introducing New Fish

Fish that have become established in an aquarium develop a natural immunity to the particular disease organisms already present in that aquarium. Any new fish introduced into the aquarium may therefore be coming into contact with disease organisms for which they have not yet built an immunity. As already mentioned, fish carry their own individual population of parasites and bacteria with them. Therefore, the introduction of a new fish may result in the existing fish also coming into contact with disease organisms for which they have no immunity. Disease organisms can also be introduced into an aquarium on plants, invertebrates, live food, aquarium decorations and even nets which have been used in more than one aquarium.


Before introducing new fish into an established aquarium, it is a good idea to quarantine them in a separate aquarium for a minimum of two weeks, Ensure the water in the quarantine aquarium is of the same pH and hardness as that of the eventual aquarium and contains aquarium salt (2 gm per litre) to reduce stress during this settling down period. The quarantine process allows gradual recovery from the stress of being moved and time for any latent disease to develop. During quarantine take the opportunity to carry out a preventative course of treatment with a Broad Spectrum Treatment (such as Interpet's Liquisil General Tonic No. 5) to clear the fish of most common disease organisms.

Regular Preventative Treatment

A general broad spectrum treatment (such as Interpet's Liquisil General Tonic No. 5) can either be used once a month to reduce disease organism levels, so swinging the balance in favour of the fish, or used at times of particular stress, e.g. when poor water quality is identified, or new fish are introduced.


In spite of all precautions, disease episodes may still occur in the aquarium. It is critical to monitor your fish regularly so that you notice any abnormal behaviour or differences in appearance which may signify the onset of disease. Prompt and correct diagnosis and treatment is the secret to increasing the chance of success when treating fish diseases.

Fish Diseases


In spite of all precautions, disease episodes may still occur in the aquarium. It is critical to monitor your fish regularly so that you notice any abnormal behaviour or differences in appearance which may signify the onset of disease. Prompt and correct diagnosis and treatment is the secret to increasing the chance of success when treating fish diseases.

Things to Look For :

Fish Appearance

Fish Appearance

Symptoms of Fish Disease
Definite Symptom Of Disease Possible Symptom Of Disease
Fish gasping. Rapid gill movement. Fish hanging near surface. Bacterial gill disease. Poisoning/Water quality
White Spot. Velvet. Slime Disease. Higher form parasite
Flicking & Rubbing White Spot. Velvet. Slime Disease. Higher form Parasite. Poisoning/Water Quality
Peppering of Gold Spots Velvet  
Patches of Slime Slime Disease. Poisoning/Water Quality  
White Spots (sugar grain) White Spot  
Disc or Wormlike attachments on body/gills Higher form Parasite  
Gills pale/eroded Higher form parasite. Bacterial gill disease White Spot. Velvet. Slime Disease
Cloudy Eyes Slime disease. Poisoning/Water quality  
Cotton wool Growths Mouth Rot. Fungus  
Fins eroded/opaque Fin Rot Internal Bacterial Infection
Mouth/Head Erosion Mouth Rot  
Eyes Swollen (Pop-eye)   Internal Bacterial Infection
Distended/Hollow Stomach   Internal Bacterial Infection
Holes/Ulcers   Internal Bacterial Infection
Fish Colour Darkens Poisoning/Water Quality Internal Bacterial Infection
Unexplained Deaths Internal Bacterial Infection  
Darting Around Poisoning/Water Quality  
Unable to maintain Balance Swim Bladder problems. Poisoning/Water Quality Internal Bacterial Infection


White Spot

White Spot is a protozoan infection caused in freshwater by Ichthyophthirius species and in salt water by Cryptocaryon species. These protozoan parasites spend part of their life cycle embedded in the skin of fish, feeding the tissue and body fluid. This on-fish stage is enclosed in a white cyst, which gives the classical (white spot) symptoms of this disease. The adult emerges from the cyst and drops to the floor of the aquarium where it forms into a protective capsule inside which it multiplies by division. Some days later the capsule bursts and releases hundreds of free-swimming infective parasites which search for a new fish host. Massive infestation, particularly of the gills, leads to respiration problems in the fish, salt balance difficulties, and eventually to death. The white spot life cycle duration depends on the temperature of the water, being only 10-12 hours at 26░C, but 3 weeks at 5░C. The white spot's free-swimming stage is the only stage of the life cycle affected by the treatment.

White Spot Treatment

A specific White Spot treatment (such as Interpet's Anti White Spot No.6) should be used. These products remain active in the aquarium for several days, so ensuring the free-swimming parasites are destroyed as they emerge from the capsules. You can assist rapid eradication of white spot by raising the aquarium temperature to 26░C, so shortening the life cycle.


This is caused in freshwater aquariums by protozoan parasite species called Oodinium and in marine water by Amyloodinium. These protozoan parasites have a very similar life cycle to white spot, however, the cysts are much smaller, being about 1 mm in diameter, and far more numerous, giving the appearance of a peppering of gold spots, or a velvet like texture to the fish's skin.

Slime Disease

This disease is also caused by protozoa e.g. Chilodonella, Ichthyobodo (Costia), Trichodina and Brooklynella species, and Trematodes (flukes) e.g. Gyrodactylus and Dactylogyrus species.

These parasites spend the whole of their life cycle on the fish, although infective young parasites may be released into the water to spread to new hosts. The parasites live on the skin and gill surface, eating gill and skin tissue debris. If their numbers increase rapidly, they may irritate the skin and gills, causing excessive mucus production and usually killing the fish by smothering the gills and hence suffocation.

Slime Disease Treatment

The correct treatment (such as Interpet's Anti Slime and Velvet No.7) quickly and effectively eradicates gill and skin parasites and removes the mucus build up, therefore aiding the fish's respiration.

Higher Parasite Forms

These come in the form of crustaceans, e.g. anchor worm (Lernaea species) fish lice (Argulus species) gill maggots (Ergasilus species) and fish leeches. These higher forms of parasites are fortunately not common in aquarium fish. Treatment for Higher Form Parasites Treatment should be with a product such as Interpet's Anti Crustacean Parasite No. 12. This powerful treatment eliminates these difficult to eradicate parasites, but should be used with care!!


Finrot is caused by Aeromonas and Pseudomonas species of bacteria found in all aquariums. The fin and ray tissue becomes opaque, blood streaked and eaten away. It is important to catch this erosion before it reaches the fin base, as this leads to the fish's death. Susceptibility to this disease is commonly caused by poor water conditions or damage resulting from fin-nipping fish. It is therefore necessary to deal with the cause of the problem to prevent a recurrence.

Finrot Treatment

Treatments (such as Interpet's Anti Fungus and Bacteria No.8) destroys the bacteria, halting fin erosion. It may take some time for the fin to grow back. The medicine remains active for several days thus preventing a rapid recurrence of this disease.

Mouthrot / Mouth Fungus

This is caused by a bacterium, Flexibacter Columnaris. The symptoms of this disease are typically erosion of the mouth, commonly associated with a fungal like growth, which is in fact colonies of the column-like bacteria. Like finrot, mouthrot is associated with poor water conditions which must be corrected.

Treatment for Mouthrot / Mouth Fungus

Treatments (such as Interpet's Anti Fungus and Bacteria No.8) destroys the bacteria, halting mouth erosion although it may take some time for regeneration. The medicine remains active for several days thus preventing an immediate recurrence.


Fish fungus is caused by fungus species such as Saprolegnia. Fungus spores are present in all freshwater aquaria. A disease outbreak is usually a secondary infection of an area of the fish's skin or gill barrier which has been damaged. A Saprolegnia growth looks like cotton wool. It is essential to prevent the fungus spreading deep into the tissue or over the gills. Livebearers are particularly susceptible to fungal problems which can usually be prevented by adding 0.1% (1 gm per litre) of aquarium salt to the tank.

Fungus Treatment

Treatments (such as Interpet's Anti Fungus and Bacteria No.8) stops the fungus spreading and destroys it. The medicine remains active for several days to ensure full healing occurs.

Internal Bacteria

These diseases are caused by a variety of bacteria species, e.g. Pseudomonas flourescens, Aeromonas hydrophila and Virio marinium. Internal bacterial infections spread throughout the fish's tissue and internal organs. Symptoms vary, depending on the acuteness of the disease. In some cases the fish will just darken in colour, become listless, stop feeding and die. In others severe symptoms exist, ulcers, abdominal and eye swelling, destruction of the central nervous system, and then the fish dies. It is essential to catch these diseases as early as possible or treat as a precaution as soon as they are suspected.

Treatment for Internal Bacteria

Previously, the only effective treatment against internal bacteria was veterinary prescribed antibiotics. New medicines (such as Interpet's Anti Internal Bacteria No.9) are now available over the counter. These easy treatment methods improve the chances of successful treatment of internal bacterial infections. Bacterial problems such as dropsy, ulcers and septicaemia are very difficult to cure if the disease is too far advanced, but the medicines will help to prevent further deaths.

Bacterial Gill Disease

Bacterial gill disease is caused by bacteria (e.g.Flexibacter species). Bacterial erosion of the delicate gill membrane causes suffocation of the fish. Bacterial gill disease often occurs after the gills have been damaged by poor water quality. Affected gills are pale or grey/brown in colour with heavy mucus production and clear signs of erosion.

Treatment of Bacterial Gill Disease

Treatment with medicines (such as Interpet's Anti Internal Bacteria No.9) plus the addition of 0.2% aquarium salt is recommended. Water conditions must be checked, as poor water contributes greatly to the onset of this disease.

Swim Bladder Problems

Swim bladder problems are caused by bacterial and viral infections, or hereditary problems. The swim bladder helps the fish to control its buoyancy, allowing it to maintain its position in the water. Internal bacterial infections can affect its function, making it difficult for fish to maintain position. Fancy goldfish with their short body form are particularly prone to this problem.

Treatment for Swim Bladder Problems

Raising the temperature to 27░C (80░F), adding aquarium salt to a level of 0.5% (5 gm per litre), and using a treatment such as Interpet's Swim Bladder Treatment No.13 is recommended. You should also feed sparingly.

Poisoning/Water Quality Problems

There are several causes for this type of health problems:

  • Poor water quality, i.e., high or low pH, high ammonia/nitrite levels.
  • Untreated tap water containing chlorine or heavy metals (copper)
  • Medications. There may have been an overdose, or a particular species could be susceptible to an active ingredient.
  • Household toxins e.g. paint fumes, polish etc.

Treatment for Poisoning/Poor Water Quality Test for ph, ammonia and nitrite using a test kit. Use carbon in the filter system or in a separate box filter in the corner of the aquarium. Carry out several large scale water changes. Ensure the tap water is treated with a conditioner to remove chlorine and heavy metals. Identify the source of the problem and eliminate it.


  • Always follow the dosing instructions on the bottle.
  • Remove any carbon from the filters before using any disease treatments.
  • Do not use more than one disease treatment at a time.
  • Keep all medicines away from children.
  • If in doubt seek advice from your aquatic retailer.

Interpet, the specialists in aquarium and pond care, have been developing and manufacturing aquarium products since 1952. Interpet's product range has been designed to achieve the goal of trouble free fishkeeping. We are indebted to them for permission to use the information on this page.

Water Quality

(Information Courtesy of Tetra Information Centre)

Creating the correct aquatic environment

We know that different aquarium fish have different preferences with regard to water quality. Of course, it would not be possible to sell ready made 'guppy' or 'neon tetra' water for obvious reasons. However, any aquarist can reproduce the desired water of his or her fish by using some of the many aquatic aids now available.

Adjusting the waterquality

In the following information, the methods for altering the water quality are provided. With toxic pollutants such as ammonia and nitrite it is important to remove the toxins as quickly as possible. However, with hardness and pH (as with temperature) a sudden change can cause more problems than leaving the fish in unsuitable water conditions. Hardness and pH should therefore be altered slowly over a period of several days in order to avoid stressing your fish and making them susceptible to disease.

Water Hardness

Water hardness is a measure of the quantity of dissolved salts that are present. Pure rainwater has very few dissolved salts and is termed "soft water". As it seeps through the rocks and soil the rain water becomes enriched with various salts. This is greatly facilitated by the slightly acid pH of rain water. If the rocks are chalk or limestone more salts are dissolved than if they are sandstone or granite. Consequently, water from limestone areas is rich in dissolved salts and is hard, whereas water from sandstone or granite areas is low in dissolved salts and is soft.

Measurement of water hardness

Different countries use different units and this can be confusing. The two most commonly used units are the German degrees of hardness ( 1░ dH is equivalent to 10mg of lime per litre of water) and American degrees of hardness ( parts per million (ppm) of calcium carbonate). To convert from ░dH into ppm calcium carbonate, multiply by 17.9.

General Hardness

The general hardness of water is a measure of the amount of calcium and magnesium salts that are present, with hard water containing more than soft water. The general hardness directly influences the internal functions of fish, plants and other organisms. The gill membranes and the skin of fish appear to be particularly sensitive to extreme hardness values. Affected fish may become slightly swollen and will rub against underwater objects╩ or "shimmy" in the water (showing a swimming motion without moving forwards or backwards). A suitable level for most tropical fish lies between 3░ and 10░ dH.

What to do if GH is too high

Dilute the hardwater with clean rain water or distilled water. Use water softening resins, provided they are safe for aquarium use. Ensure gravel is lime free, as limestone gravels will increase water hardness.╩

What to do if GH is too low

Add limestone pieces, cockle shell or coral sand into the filter or aquarium, until the required level is obtained. Marine salts can be used where a high GH is required for brackish water or marine fish.

Carbonate Hardness KH (Temporary Hardness)

As well as calcium and magnesium, most natural waters also contain bicarbonates as part of the total salt mix. It is these bicarbonates that make up the carbonate hardness or KH value. The bicarbonates have an important function in the overall chemistry of aquarium water. They act as a pH buffer preventing sudden changes in the pH value. Where bicarbonates are deficient ( i.e. low KH value), large fluctuations in the pH can occur under certain circumstances and the addition of a small amount of acid or alkaline water will cause a drastic change in the pH of the aquarium water. The higher the KH the better the pH buffering, but a very high KH can lead to a markedly alkaline pH. Carbonate hardness is also known as temporary hardness because bicarbonates change to carbonates and come out of solution when the water is boiled. Recommended values of the KH for stable conditions are around 2░ to 8░ dH, although certain fish do have other requirements.

What to do if the KH is too low

Make up a strong solution of sodium bicarbonate and add it to the water a little at a time, until the desired KH is reached. Ensure water is well aerated during this process. Do not add the sodium bicarbonate solution directly into a tank containing fish or plants, as the sudden change may adversely affect the fish and plants. The adjustment should be made to water outside of the tank, and the adjusted water then added slowly to the aquarium. This should be carried out slowly over a period of several days, closely monitoring the pH during the adjustment.

What to do if the KH is too high

Dilute the hardwater with clean rain water, distilled water, previously boiled water, or water treated with a commercially available softener. If practical, the tank can be filled with boiled water that has been cooled and aerated

Acidity, Alkalinity and pH

The degree of acidity or alkalinity of water is expressed in terms of the pH, which ranges from 1 (acidic) through 7 (neutral) to 14 (alkaline). The pH value is calculated from the total acid and base substances found in solution in the water. At a pH of 7 the acid substances cancel out the base substances, hence the water is termed 'neutral'. Bicarbonates in the water are important as they are able to bind with excess acids or bases and so prevent major pH fluctuations. A pH of 6.5 to 7 is suitable for most tropical fish species, but there are some exceptions.

What to do if the pH is too high

The pH of the water may be reduced by adding peat to the aquarium or filter. Approximately 2 handfuls of peat, placed loosely in a fine mesh bag, should be added to every 2-3 gallons of water for several days before adding the water to the aquarium. Commercial pH adjusters are also available, but great care must be taken not to alter the pH too rapidly, as it could prove fatal to the fish

What to do if the pH is too low

Water may be made more alkaline (increase the pH) by adding limestone, coral sand or sodium bicarbonate to the water. This will also increase the water hardness, but most species that prefer alkaline water also require hard water.

Whichever method you choose Any pH changes must be conducted slowly, over a period of several days to avoid stressing the fish. Always change the pH outside of the aquarium except when material is added to the filter) to avoid any sudden fluctuations.

Nitrogen Cycle

Within the aquarium, fish waste together with any uneaten food and dead plants is decomposed in a process known as the nitrogen cycle. The nitrogen cycle involves the breakdown of fish waste, uneaten food etc. into ammonia or ammonium, ammonia or ammonium into nitrites, and finally nitrites into nitrates. Each of these stages is accomplished by means of bacteria in the presence of oxygen.

Ammonia and Ammonium

The first stage in the decomposition of fish waste and uneaten food is the formation of toxic ammonia and the relatively non-toxic ammonium. Both are easily converted into the other with the ratio of ammonia to ammonium being largely dependent upon pH. At a high pH (above 8.5) - mostly ammonia (toxic) At a low pH (below 7.5) - mostly ammonium (non-toxic) At levels as low as 0.25mg ammonia per litre of water, ammonia can be lethal to the fish, therefore regular tests should be undertaken in order to prevent it reaching toxic levels. In an established aquarium the ammonia concentration should be very close to 0mg per litre . If it is not suggests that:

  • The filter or tank has been recently set up and has not matured.
  • The aquarium is overstocked.
  • The fish are being overfed.
  • The filter is not functioning correctly.
  • There is excess organic debris somewhere in the aquarium.

What to do if the Ammonia content is too high

Immediately change one third of the water in order to remove some of the toxic ammonia. At the same time remove as much debris as possible from the aquarium and gravel. Increase aeration if possible and investigate the cause of the problem. Commercial products, such as activated charcoal and zeolite are available which can be added to the filter and which effectively remove ammonia. Methods of maintaining a low ammonia level are dealt with in the section on nitrites.


Nitrite, the second stage in the nitrogen breakdown process is also poisonous to the fish. For this reason it too should be regularly measured in order to keep it under control. As far as possible the nitrite concentration should not exceed 0.2mg per litre of water. At a level of 0.5mg per litre the fish will be adversely affected. Raised nitrite levels are often an indication that the nitrogen breakdown system has been disturbed. They are usually preceded by increased ammonia or ammonium levels and the causes are the same. As with ammonia, immediately remove one third of the water, together with any debris from the aquarium and gravel. Replace it with conditioned tapwater of the same temperature, and investigate the cause of the raised nitrite level.

What to do if the Nitrite content is too high

Nitrite levels may be kept low by the following means:

  • Carry out regular partial water changes (20-30% of the water every 2-3 weeks) removing any debris that may have accumulated in the aquarium or gravel.
  • Increase the biological filtration.
  • Undergravel filters should be cleaned by using a gravel cleaner to remove debris from the gravel, and thus preventing it from becoming blocked. Occasionally the syphon tube should be placed down the uplift tubes of the filter to remove debris that has accumulated under the filter plates. The filter media from box filters and power filters should be rinsed in old aquarium water to remove excess debris. Do not rinse under the tap as the chlorine will kill the helpful bacteria. Clean the filters at each water change.
  • Maintain a sensible stocking level and feeding rate. The fish should generally be fed once or twice a day on as much as they will consume within 1-2 minutes. The recommended maximum stocking rates for various aquaria are as follows :

Tropical freshwater aquarium - 1 inch (2.4cm) of fish length excluding tails for every 12 square inches (72cm2) of water surface area.

Coldwater Aquaria - 1 inch (2.4cm) of fish length excluding tails for every 24 square inches (140cm2) of water surface area.

Where does Nitrate come from?

Nitrate is the final product of nitrogen decomposition and, in comparison to nitrite and ammonia is considerably less harmful to the fish. Nitrate accumulates in the water and will be used up by the plants and algae to a certain extent. Consequently, it promotes plant growth, but in excess quantities it can also lead to an undesirable growth of algae. In almost all situations the nitrate is not absorbed completely by the plants. And in time, will accumulate in the water. Raised nitrate levels can be controlled by regular water changes, by the use of chemical filter media, or by encouraging dense healthy plant growth and shifting the ratio of fish to plants more in favour of the plants.

  • Nitrate levels Below 12.5 mg nitrate : clean water : very good for fish and plants
  • 12.5 - 25 mg nitrate : water still quite good : good for fish and plants
  • 25 - 50 mg nitrate : partial water change advisable : still satisfactory for plants
  • 50 - 100 mg nitrate : change of water necessary : stagnation of plant growth. Growth of blue/green algae commences.
  • Above 100 mg nitrate : water extremely polluted and no longer╩ wholesome for plants. Dangerous to fish. : In absence of oxygen, nitrate can easily turn into toxic nitrite. At these levels of nitrate, tests for nitrite should also be carried out regularly.

Reverse Osmosis

What is Reverse Osmosis?

Reverse osmosis is the finest filtration known. It allows the removal of particles as small as ions from a solution. Reverse osmosis is used to purify water and remove salts and other impurities in order to improve the color, taste or properties of the fluid. The most common use for reverse osmosis is in purifying water. It is used to produce water that meets the most demanding specifications that are currently in place.

Reverse osmosis uses a membrane that is semi-permeable, allowing the fluid that is being purified to pass through it, while rejecting the contaminants that remain. Most reverse osmosis technology uses a process known as crossflow to allow the membrane to continually clean itself. As some of the fluid passes through the membrane the rest continues downstream, sweeping the rejected species away from the membrane. The process of reverse osmosis requires a driving force to push the fluid through the membrane, and the most common force is pressure from the mains water supply. The higher the pressure, the larger the driving force and the easier it is for the fluid to be forced through the membrane.

Why do I need to Use Reverse Osmosis Water?

The water in our taps is contaminated with all sorts of toxic materials and these substances can be toxic to aquarium fish. Excess nitrates and phosphates can encourage algal growth, and hardness can affect the ease of controlling the pH of the water. If you use R/O water from the start, then you can add back the required amount of minerals and salts for the specific needs of your tank inhabitants.

Why use a TFC Membrane?

The thin film composite membrane can remove a larger percentage of contaminates from the water. Listed below are the typical removal percentages (actual percentages will vary depending on the exact chemistry, temperature, pressure and TDS of your water):

  • Hardness : 93-98%
  • Heavy Metals : 95-98%
  • Ammonium : 80-90%
  • Phosphate : 95-98%
  • Nitrate : 90-95%
  • Silicate : 80-90%
  • Bacteria : >99%

Why Doesn't the Unit Produce the Amount of Water it Should?

Water Pressure : The ideal water pressure should be 65 psi. Water pressure at 45 psi will reduce the rated gallons per day production by half.

Water Temperature : The ideal operating water temperature should be 70 - 77 deg. F (21 - 25 deg.C). Low water temperatures such as 50 deg.F (10 deg C) will again restrict the output to about half.

Total Dissolved Solids : The units are rated for 200 ppm (parts per million) of TDS. High TDS can also lower product water output

Can I Use Hot Water?

No : NEVER run hot or a mix of hot/cold through the unit. Use only cold water.

Do I Need To Flush a New Unit?

The membranes are shipped almost completely dry to preserve them in shipment. The unit should be run as normal, but the first 10-12 gallons of product water should be discarded. After this, the water is ready for use. As it takes up to 10 days of continuous running for the new membrane to fully hydrate, the output during this period may be reduced from the rated output, but the product water is still properly filtered and can be used as normal.

What Do I Need To Do If I am Not Using the Unit Permanently?

The membrane is extremely delicate and must not be allowed to dry out once hydrated.

For short periods of non-use, the membrane can remain installed in the unit, but the pipe work must be fitted in such a way that water is always trapped within the membrane housing so it does not dry out .

For longer periods (say 3-4 weeks) of non-use : the membrane should be removed from the unit and stored with 2 tablespoons of product water in an air-tight, sealed plastic bag, and placed in the refrigerator. DO NOT ALLOW TO FREEZE. After re-installation, the first 1-2 gallons of product water should be discarded

The Unit Seems to Produce a Lot of Waste Water

Unfortunately, Reverse Osmosis units only produce about 1 gallon of product water for every 4 gallons used. So 3 gallons of it goes to waste (Figures are approximate). So if you are supplied with metered water, so may need to consider the implications, and hence the cost, of R/O water production prior to making any decision.

How Long Does the Membrane Last?

Used under average conditions, the membrane can filter about 25,000 gallons of water : or about 3-5 years of service.

However, TFC membranes can be damaged by Chlorine, so proper maintenance of the sediment and carbon pre-filters is essential.

(We are indebted to QualityPure Reverse Osmosis manufacturers for permission to use the information contained above)

Koi Pond Construction

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