de filter keeps clogging

[barb]

we are at a loss as to why our filter keeps getting clogged. we bought a new de grid filter as last year we had similar problems as we thought the filter was the real problem. we've opened our pool and have cleaned the filter once - which we expected. but now, only 10 days later, it's clogged again. the sanitizer that we are using is revacil. in addition to the clogging problems, in the last 10 days we have put in 3 times of the amount of required shock over the last two weeks and the shock level is registering zero when the water is tested.