Not here with a question. Instead I'm sharing with readers (esp DIYers) how I solved my pool's mysterious problem and what I learned. This forum has been very helful to me. Keywords would be: D.E. backflow skimmer drains D.E. not sticking grids fall off grids plume cloud pump shuts off back into pool Hopefully webbots will pick up for searches.
Last year I replaced my 20+ year old DE pool filter with another DE filter. Has performed great. Recently it was time to change my DE. Followed the mfgr's instructions, let it run for about half an hour and then powered it down. All was well. Until I went back to have a look about 30 minutes later.
There was a big plume of DE coming out of the skimmer and into the pool. Note: the DE wasn't going into the pool through the returns, and wasn't going into the spa. It was slowly migrating backwards from the filter into the pool through the skimmer and drains. After running the pump long enough to clear the intake pipes (skimmer/drain) --- and then switching the pump off --- I could see the plume appear in the filter basket, visible through the clear pump lid, as it started its migration backwards, a few seconds after the pump would shut off. I thought I must have done something wrong when changing the DE, so I did it again. Same result. Couldn't figure out what had changed, or why the DE wasn't even sticking to the grid the way I was used to. (BTW, turns out that DE doesn't stick to all mfgr grids when the pump turns off, and that this doesn't seem to be a big concern among pros. But why did it start this odd behavior of flowing backwards in a cloud when the pump turned off?)
Here's what I figured out: When the pump switched off, the spa --- which is only slightly higher than the pool --- was draining backwards through the returns, back into the filter, and from there past the pump and out the pool intakes (skimmer & drains). But there was still a mystery: what had changed? I didn't see a check valve between the filter and the spa already installed and so wondered: why did the system work fine all these years before with no check valve, and now it has a problem with backflow?
Answer: the system did in fact have a check valve... 1990 style. See the photo. I had been looking for a prominent modern looking check valve with a view glass, but the old check valve was passing for a connector. And for some reason it decided to go bad when I changed the DE. Had a pool guy change it out and problem went away, no more backflow.
Lesson: Modern pool components may look very different from decades old components.
Last year I replaced my 20+ year old DE pool filter with another DE filter. Has performed great. Recently it was time to change my DE. Followed the mfgr's instructions, let it run for about half an hour and then powered it down. All was well. Until I went back to have a look about 30 minutes later.
There was a big plume of DE coming out of the skimmer and into the pool. Note: the DE wasn't going into the pool through the returns, and wasn't going into the spa. It was slowly migrating backwards from the filter into the pool through the skimmer and drains. After running the pump long enough to clear the intake pipes (skimmer/drain) --- and then switching the pump off --- I could see the plume appear in the filter basket, visible through the clear pump lid, as it started its migration backwards, a few seconds after the pump would shut off. I thought I must have done something wrong when changing the DE, so I did it again. Same result. Couldn't figure out what had changed, or why the DE wasn't even sticking to the grid the way I was used to. (BTW, turns out that DE doesn't stick to all mfgr grids when the pump turns off, and that this doesn't seem to be a big concern among pros. But why did it start this odd behavior of flowing backwards in a cloud when the pump turned off?)
Here's what I figured out: When the pump switched off, the spa --- which is only slightly higher than the pool --- was draining backwards through the returns, back into the filter, and from there past the pump and out the pool intakes (skimmer & drains). But there was still a mystery: what had changed? I didn't see a check valve between the filter and the spa already installed and so wondered: why did the system work fine all these years before with no check valve, and now it has a problem with backflow?
Answer: the system did in fact have a check valve... 1990 style. See the photo. I had been looking for a prominent modern looking check valve with a view glass, but the old check valve was passing for a connector. And for some reason it decided to go bad when I changed the DE. Had a pool guy change it out and problem went away, no more backflow.
Lesson: Modern pool components may look very different from decades old components.
