Algae Magnets come in two parts.
Both contain magnets : one half of set has coarse algae removal material on its face, and the other has a soft non-scratch material.
The coarse faced magnet is placed on the inside of the aquarium glass, with the soft faced magnet on the outside. Moving the outside one across the face of the glass drags the inner magnet with it, thereby removing the algae from the inside glass as it moves.

Small Algae Magnet : approx. 2½" x 1"

IT FLOATS !    IT CLEANS !

IT'S MAGNETIC !  IT'S THE MAG-FLOAT

Now there's no need to get wet when cleaning the glass if the magnet falls off!

The Mag-Float just floats!!!!

Available in 3 sizes :

Small  : 60mm x 30mm : up to 114 litres : 5mm glass thickness

Long   : 95mm x 35mm : up to 473 litres : 10mm glass thickness

Large : 85mm x 65mm : up to 1325 litres : 16mm glass thickness

From Bakker Magnetics
Son, Netherlands

If the cleaning magnet falls off into the tank : it floats!!

Sizes as follows :

Small : 6cm x 3cm

Medium : 8cm x 3cm

Large : 10cm x 3.2cm

Xlarge : 9.5cm x 5.5cm