new filter, de returning to pool


Active member
Jun 5, 2016
Richboro, PA
Just had a new Pentair fans de filter installed. When I add DE after backwashing, there is an initial cloud of DE that flows back into the pool through my return lines upon start up.
I questioned the pool store who applied and installed the unit, and they state that I must have added too much DE.
One of the reasons I purchased a new filter was because the old one did the same thing, even after installing new grids.
I am otherwise happy with the new filter as it replaced a forty year old dinosaur. Things today are much advanced.
However, this explanation regarding DE re-entering my pool does not make sense to me as I have always thought that the only path back to the pool would have to be through the filter grids if they are in good condition.
I would think that, at most, too much DE might raise the filters operating pressure or possibly clog the grids, but can't imagine how a filter could text excess DE and route that excess to my return lines.
Your thoughts would be appreciated.

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
Rancho Cucamonga, CA
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-45
I think what you're seeing is normal for DE filters if it only happens after cleaning/backwashing. A little DE may escape through clean grids and the air bleed screen before they're coated with DE. It always happens to me when recharging the filter after a full cleaning, regardless of how slowly I add the DE slurry.

To avoid the DE entering the pool, I drop the water level in my spa by about 1/3. When adding the DE, I set suction from skimmer and returns to spa. I then set the valves to spa mode and allow it to run for about 20-30 minutes until the DE clears. It keeps the pool from clouding up and the spa clears pretty quick.


Active member
Jun 5, 2016
Richboro, PA
Thanks for your reply. Your experience mirrors mine during the forty years I have spent with this pool. However, this season, my original filter (also forty years old) would not clear my pool. Local pool dealer told me to check for DE in the pool. I had a ton of DE in the pool. After replacing the entire grid system unit, the problem did not go away, so, ultimately, the dealer recommend a new filter. I will never understand what failed/wore out in my original filter. It is not a complicated piece of equipment, and except as you describe (grids passing a small amount of DE upon initial start-up after "recharging"), there should be no way for DE to get back into the pool unless grids are worn or torn. But, new grids did not solve my problem.

That's why I became concerned after installing a brand new filter that there was still some DE getting back into the pool.

Yesterday, I back-washed/recharged and there was absolutely no DE discharged into my spa when I restarted the filter, so I feel much better now.

Thanks again for your reply.

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