Pentair FNS Plus 36 DE Filter questions/concerns

[BallstonSpaKW]

OK - since 2 years ago when I queried why my 13 year old pool was cloudy after opening and getting rid of the green (algae and organic matter), it was explained to me probably something broken inside my filter. After a few questions back and forth it was determined that other than backwashing, I had never opened my filter for inspection. A few rounds of shock, horror, and criticizing, I accepted the groups collective wisdom and vowed to check it each fall from then on. I also opened the filter, where I discovered a crack in the top of the manifold. Since everything else was also 13 years old and I was in a hurry, I purchased the entire subassembly and replaced it, along with the large tank gasket and the small gasket to the manifold. Problem solved.

Now, forward ahead 2 years to the beginning of this year (about 10 days ago). Opened another year of green pool (we have a trampoline/semi-porous winter cover and lots of early tree droppings so it is difficult to get it opened without green). Added some chlorine for a few days and the green went right away. Okay, but the pool had that cloudy look again. I had opened the filter in the fall to clean it out and everything was working normally at closing, so maybe another plastic part had cracked over the winter. A quick inspection yielded no obvious failures, but there was lots of DE caked between the filter elements, some on the top, and lots in the bottom of the filter holder under where the elements sit. Trying to get the pool opened for Memorial day, I bit the bullet and purchased a whole new subassembly and figured I could trace down just the parts that were actually broken later. So I stopped the pump on Sunday evening until the part arrived late yesterday afternoon. The pool was now clean enough to run the robotic cleaner, so I threw that in while I was replacing the filter elements. Kind of as expected, after I was done replacing the filter and had cleaned the robot it was full of DE - very gray slurry in the robot filter, which verified I had some kind of leak. While taking apart the pool filter I noticed DE again at the bottom of the filter container under the black tube and lots all over the filter elements, some caked on. But I didn't take very long to examine it - just put the new one in and turned on the pump around 7PM Tuesday evening.

The pump only runs for a couple of hours overnight, then runs from 8-10 AM and then noon-7PM. Anyway, I wasn't too worried as I was pretty sure I had corrected the problem. But now I am not so sure. After it had run for about 7 hours since last night I had a little time, so I did a careful inspection of the old filter, and couldn't really find anything wrong/broken. Another pass of the robot yielded almost no DE, but the pool still looks cloudy (pretty clean in the shallow end but I can't see the main drain in the deep end). Now it's been running less than a day so I don't want to panic yet, but...

I opened the filter just because I was curious and found the following: almost no DE clinging to the individual membranes, a little bit sitting pooled together on the bottom of the plastic cage and most of it pooled together under the filter element and the black tube on the very bottom.

Is that normal? How and where is the DE supposed to accumulate? I don't see any evidence of water or air leaks, but could something be roken in the big tube that go from the inlet to that manifold? Anyway, I am puzzled and would still like to be able to swim on Monday.

Thanks for any insight or ideas anyone may have.

Kevin

 

[SoCalGuy]

Try filtering without running the cleaner until the water clears.

 

[Richard320]

DE can fall off the grids when the pump is off. When the water hits it again it will blow it into circulation and it will coat the grids again. In theory, the heavier sand and whatnot would stay on the bottom and the DE will coat things, but as stuff gets old it sticks to the grids. You've seen it yourself when you open it.

If the pressure is okay and there's no DE in the pool, I'd say it's working.

Haziness is caused by algae more often than not. I'd try an Overnight Chlorine Loss Test to check. You might be filtering out the dead stuff but more is growing to take its place.

 

[BallstonSpaKW]

OK - after deciding I have had enough of the mess and hassle of dealing with DE, I decided to replace the DE filter with a cartridge filter. I went with a Pentair Clean & Clear Plus 320 square foot filter. Problem solved - water is now nice and clear again and I know how to deal with this unit. But while the new filter was being installed I think I found the source of the original problem, although I still don't exactly understand. The push-pull valve on the outside of the filter which lets you switch the flow to do backwashes had broken internally - the gaskets were dislodged and parts were located in places they were not supposed to be. I never found any DE or water in that area but that's the only thing I can think of. Anyway, since I plan on replacing the liner in the spring and using the pool for at least another 15 years I am still glad I now have a cartridge filter. Thanks for the assistance.

Kevin