I am running a fluval 304 canister on my 56 gallon tank. I currently have 6 tetras black fin skirts and 6 corie cats. Have a sand substrate. Been running the tank for close to 2 months. Been performing 25% water changes weekly. My water is constantly cloudy. we do a water change and its clear for maybe two days. then it gets cloudy again. I am not sure the filter media is correct. I have bio balls carbon and polishing cloths. I had hoped with this filter I would have the clearest water but my old setups with hob filters where all ways clearer. I plan on adding some more tetra variates but I want the water to be clear first before I add more fish.