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Thread: Help diagnosing peculiar behavior of DE filter

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    Join Date
    Jul 2015
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    Help diagnosing peculiar behavior of DE filter

    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.


    25,000 gal, in-ground, plastered gunite, Pentair NSF 60 DE Filter

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    Mod Squad jblizzle's Avatar
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    Re: Help diagnosing peculiar behavior of DE filter

    Sorry for the delayed response.

    First, there is no way DE should be able to back up all the way through the pump and into the skimmer and floor drain.

    1. After a full manual tear down, you should add the recommended amount of DE. After just a backwash, only add about 80%.
    2. You should tear down the filter yearly (DE Filter Cleaning Tutorial), but a regular backwashing should be fine.
    3. Yes. You may also want to check your multi-port gasket as that could be allowing DE to pass.
    4. Not sure what this would accomplish.

    The algae in the site glass is no big deal. Since it should only be getting water when you run in backwash or waste or clean and is not connected to the pool water normally. If it is staying wet and full of water, you may check to be sure the spider gasket is not always leaking.

    The only way for DE to backup into the pump/pool is if there is a leak in the filter that allows it to drain backward when the pump turns off. If the system is properly sealed, the pump and filter should stay full of water when the pump turns off.
    Jason, TFP Moderator
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  3. Back To Top    #3

    Re: Help diagnosing peculiar behavior of DE filter

    The multiport gasket is likely to be bad. Listen at the waste line when the pump is first turned off. Listen for the sound of air being sucked in. If the waste line is hard plumbed, remove the sight glass and listen there.

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    Isaac-1's Avatar
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    Re: Help diagnosing peculiar behavior of DE filter

    2 things, first I had a problem with my Hayward Perflex DE filter backing up into the skimmer when the pump was off a couple of months ago, problem turned out to be a bad integrated check valve on the filter inlet, I added a Jandy check valve inline before the filter and it seems to have cured the problem. One advantage of the Jandy check valve is that it is serviceable without disconnecting all the plumbing going into the filter.

    Second topic, Don't trust those scoops, the weight actual weight they hold can vary about 30% depending on how you pack them since DE is very light and fluffy, I would suggest investing a small digital scale, when my 20 year old digital postage scale died last year I replaced it with one from Amazon, I think the price was under $15 for a scale that reads up to around 10 pounds with 1/10 ounce increments. In fact I found that my major chain branded 1 pound DE scoop would only hold about .9 pounds no matter how much I tried to pack it
    Indoor 20x40 35,000 gallon vinyl pool with 1.5 HP 2 speed Jandy FloPro pump, Hayward EC75 Perflex DE filter, 11 4x12 Techno-Solis solar panels w/ Aquasolar controller, Aquabot Turbo T Robot Cleaner. Also LMI metering chlorine dispenser pump and HotSpring Jetsetter
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    Re: Help diagnosing peculiar behavior of DE filter

    There is a simple resolve to this problem and that is to install a check valve between the filter and pump. THAT IS NOT MY RECOMMENDATION!. There is air in your system that is being drawn in when the pump is turned off. Most likely this would be a physical leak while the pump is running. I agree with the previous posts in regard to the spider gasket but your waste line normally would leak. Pay close attention to the 3 port valves and listen for any changes when the pump is immediately turned off and on. If nothing is noticed unfortunately you may need to look into a pressure test on your plumbing system.
    Your pool equipment is above the water level of pool for most applications and if the water is reversing back to pool on the suction side air is being introduced above the water level of pool. Swimming pools are closed water systems unlike irrigation which is open. That being said any plumbing above the water level can be the problem. Have any plants been planted lately? If so check that out.
    Service Manager for Gracia & Vigil. Specialize in concrete pools, commercial and residential, but if the pool is in the ground I can fix it!

  6. Back To Top    #6

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    Help diagnosing peculiar behavior of DE filter

    Thanks for all the insights. The multi port is actually pretty new, so it is unlikely to be the problem. The sight glass has been full of water as long as I remember. Is that a big "no no"? Thanks!


    25,000 gal, in-ground, plastered gunite, Pentair NSF 60 DE Filter

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