What is DE and do I need to add some to my sand filter? I have seen in here where some are adding it to their filter to help clear the water. What about clarifier? I have added bleach and kept the FC levels way up since Thursday and have seen virtually no change at all. Is this something that will finally just clear up overnight or is it more gradual?
Update on my problem: (27000 - vinyl - swg)
Water is clean and clear, but just a little cloudy. It only seems to be noticable in the deep end due to the depth, I guess.
pH is 7.6
FC is somewhere around 20 (cheap test-dilution method - waiting on Ben's)
cya seems to be very high now - about 90 (again cheap test)
vinyl pool so I haven't been too concerned with Calcium Hardness
Alk is around 100.
Pool store said I don't have any CC, but my cheap test doesn't check for them
I can't lie, I am getting VERY VERY frustrated. I hate going out there because I know it is going to look the same. It can't be in very bad shape because it has been absolutely perfect for the past 3 years. Now this...

Any help or direction would be GREATLY appreciated.
Brad