Silt on pool bottom from filter

Hi everyone :)

Another year, another (ongoing) problem. Our sand filter is dumping silt in the bottom of the pool. The water is crystal clear and so is the bottom as long as we don't run the pump. This has been a problem in varying degrees since we installed the pool in 2006. This year it has gone crazy! We are vacuuming to waste all the time so we don't recycle the silt back into the pool, and it doesn't make a difference. We replaced the sand (with #20 silica) and checked the lats two years ago to see if that was the problem. Everything was fine and dandy inside. This year we had a guy come out with sonar because we had a leak somewhere in the vinyl...there were in fact eight! :O
So now we know for sure there isn't any dirt leaching to the bottom from a hole. Last week we didn't use the pool because the weather turned, so we didn't run the pump for two days. The bottom was clean, until the third day when we turned the pump back on. We are back to running the pump 6-8 hours a day, every day, and back to vacuuming to waste every day to get the bottom clean. The water itself isn't getting mucked up, you can very clearly see the silt on the bottom of the pool. We know it's not sand because it doesn't sit and stay, if you get near it, it poofs into the water. If you touch it, it isn't slimey, just silty, and we know it's not algae. If we can't find a solution we'll have to buy a new system because we're losing too much money on chems and water vacuuming to waste all the time. The only causes I could find online were for the pump being too big for the filter, or too much sand in the filter but according to our owner's manual they are the correct sizes to work with each other, and we measured the sand very carefully when we replaced it. Any ideas or help will be greatly appreciated! Thanks in advance :)

FC 4.0
CC 0
Ph 7.4/7.5
Alk 190 (it's our local water, but since we're vinyl, eh)
Calc we don't test
CYA 30

Also, we tried using DE last summer to see if that helped...it didn't.