Moved from another thread to prevent hi-jacking.
I wasn't sure what caused it, but it took me about 3-4 weeks to get it clear again.
I thought it might have been baking soda, but it might have been PH up or CYA. What I could tell for sure was the bottom 2 rungs weren't clearly visible, even though all the test were good with FC at 5.8, and CYA at 35, PH at 7.6, and I could see little tiny sparkles at night, if I held my really bright flashlight at the surface shining down. It also felt slimy or slick from the waterline down with a 1-2 inch wide band of white at the waterline.
I tried Super Blue, and even phosphate remover, with a combination of 24/7 filtering and adding DE to my sand filter and back flushed every time the filter pressure climbed above 20psi ( thats 5 psi over normal, with the robot running, and it quits flowing as much as usual). With a good brushing of the sidewalls, and scotchbright at the waterline.