I will have to check the sand. I know the filter and pump were replaced about two years ago but there is still no telling what is in it. I know that when I try to vacuum algae some blows through and the water becomes more cloudy. I tried to test it with DE though and didn't notice any of that coming back in through the return.

Added bleach last night to 15PPM, this morning tested 14PPM and no sign at all of CC.