I have 2 x yellow bellied sliders in a 75 gallon tank and cannot keep the water clean. I have filters, a heater the correct lighting and the turtles seem happy enoughbut the water alwayslooks horrid. I use AquaSafe, and I'm liberal with the API sludge remover and PRIME water conditioner. I have another reptifilter arriving Wednesday. What am I not doing right?