probably just diatoms then. it will clear up but as long as you keep using tap water you will have this problem. my lfs has a constant diatom bloom. all they use is tap water. switch to ro water instead of tap.
You can get a diatom filter for about $70, way less than an RO. Just use it on the water your gonna put in. Thats the only thing its good for, but if thats your only problem...