I have a 40gallon freshwater tank with a pair fire mouths a pair rainbow chicilids a texas cichilid a pair clown loaches a bristlenose and a few peppered catfish. I only feed sparsely twice a day. I have a internal filter which cleans 650litres an hour, an external cannister which cleans 680 litres an hour. the medium includes ceramic rings and foam for pre filtering then 100 micron wool for finer mechanical filtering followed by good quality carbon finished with bio rings from Hagen. The internal is running various sized foam inserts. I siphon the gravel once a week and change 20% of the water. Now I have to admit my water is clear, but when I go to my local fish shop he has several tanks which are CRYSTAL CLEAR. Can anyone give me an idea of how this is achieved.