Hello. I have a 125 gallon tank with four 6" caribes. I do weekly water changes and have excellent filtration. No matter what I do, every few days the water gets a yellow tint to it. It looks cloudy. The only way to fix this is to change almost ALL the water; but I'm hesitant to do this cuz I don't wanna shock my fish. I'm having a very hard time keeping the water crystal clear. The only additives I've used are things similar to Novaqua. Whether or not I treat the water, I keep getting the same yellow/brownish color. Does anyone know what is going on with my tank? I don't want to lost $400 worth of fish...THX!! 

