I had the same problem at one time and thought I had fixed it. The last two years I kept getting DE in the pool(only have had the pool for 5). The last time my air breather was bad and I replaced it to no avail. I inspected everything and still DE in the pool. I narrowed it down to the spider gasket.

I found DE in the pool to be very discomforting becuase it was nickle and diming me to death. I was so fed up with getting DE in the pool I decided to make the plunge and replace it with a new 30" sand filter with zeo-sand (it filter to 3 mirons the same as DE) and it works great!! It has less maintenance and will last a long time without the annual mess of tearing appart and cleaning.