Hello all! So I am a recent convert to the TFP method and needed your help diagnosing some peculiar behavior I'm seeing with my DE filter (Pentair Nautilus FNS 60).
Whenever I charge fresh DE after a backwash, I get some DE in my pool returns for a few days. I usually vacuum it up over a few days and the problem fades away. When the pump stops running, I see some DE back up from the main drain and skimmers and DE in the pool strainer basket, but it usually disappears soon after the pump starts back up. I have lived with this problem as it is but a minor annoyance.
Fast forward to 1 month ago, a few weeks after I switched to the TFP method. I SLAMed my pool to get rid of a mustard algae problem, and then backwashed the filter and charged new DE. Pool has been looking great and all I'm having to do is add liquid chlorine a few times a week and muriatic acid once a week to keep things humming along.
Fast forward to last week. I notice my chlorine levels drop faster than expected, and CC go up a bit. No biggie. However, I happen to notice that the sight glass near my multiport valve is full of green algae. I immediately flushed the line by running the pump in the "Waste" setting and it cleared quickly. However, I began to suspect I had some algae in the filter.
Fast forward to yesterday. I decided to take apart the filter and clean out the grids. To my surprise, they were almost pristine with no algae at all. When I took out the filter grid assembly, the DE at the bottom was 3 inches deep. Also, I noticed the air bleed strainer wire mesh had been pushed in and was full of DE, and thus mostly occluded. I cleaned out the grids, lubed the o-rings, and reassembled the filter. I noticed the o-ring on the standpipe was a bit stiff. Then I flushed the lines but running the pump with the multiport in the "Waste" and "Backwash" setting for 10 minutes each. This morning, I charged the correct amount of DE (11 scoops ~ 7.5lb instead of 15 scoops I had been charging per pool store instructions) through the near skimmer. While doing so, I noticed the spa return had air and the spa was getting cloudy, but the pool returns were fine.
My takeaways are below. Would appreciate if you can review for accuracy and add any other insights that I might have missed. Thanks in advance!
1. I've been charging too much DE (15 scoops instead of 11)
2. May be better to back wash the filter manually rather than rely on the automatic option.
3. Replace the o-ring on the standpipe. Could be allowing DE to leak through.
4. Flush the spa return line.
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