Interpet filter aid no3 100ml polishes aquarium water to make it crystal clearr however good your filtration system there are always minute particles present which find their way through the finest filter mediar these particles irritate fish gill membranes stunt plant growth by filtering out light and ruin the enjoyment of seeing your fish in their full gloryr interpet no3 filter aid acts rapidly clumping the fine particles together so that the filter can remove them producing crystal cl