I have a 55g tank with sand substrate. I am running a dual Penguin Bio Wheel on one end of the tank and a single Penguin Bio Wheel filter on the other side of the tank. I let the tank cycle for 8 days and had crystal clear water. After adding 6 fish I immediately had cloudy water. Is it because they are digging in the sand and just kicking it up or something else. I have been in the hobby for 12 years and never had this problem before. Also I should add this is a first time using sand. Any suggestions or comments would be appreciated!!!