Interpet Filter Aid No.3 100ml polishes aquarium water to make it crystal clear However good your filtration system, there are always minute particles present which find their way through the finest filter media. These particles irritate fish gill membranes, stunt plant growth by filtering out light and ruin the enjoyment of seeing your fish in their full glory. Interpet No.3 Filter Aid acts rapidly, clumping the fine particles together so that the filter can remove them, producing crystal clear water. For use in coldwater and tropical freshwater systems. One 100ml bottle treats 500 Litres