I have a 90 gallon tank with 2 R.E.S., 1 14" and 1 7" I operate a top line filtration system, I cycle the water, habitat has platform and basking light, and aquatic gravel rock, and aquatic larger rock with app. 65 gallons of water. Treated as required. This tank has always maintained flawlessly, and now it will not stay clean, and the odor returns in a few days. I have completely cleaned, filled, and treated this tank. This is unexplainable. I am not a novice so it really has me dumbstruck. Can anyone help please?