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Thread: Water pressure low while filtering

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    Join Date
    May 2016
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    Westhampton Beach, NY
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    Water pressure low while filtering

    Dear experienced pool maintainers,

    This is my first pool. Underground vinyl pool, 20'x15'-ish, 6 years old, not maintained for 5! Never winterized. Thriving frog population.

    Water level was at the top of the skimmers. No pressure test done but I assumed the high water level was an indication of good plumbing. Pump was gone, filter was gutted.

    We skimmed out a bunch of solids at the bottom, emptied about 2' out then cleared away the bottom intake and refilled with the hose.

    Installed a 1.5h pump and a new 2024 DE filter while reusing the original plumbing and muliport (but replaced the gasket).

    We then shocked the pool with 4 gallons of shock and put a bunch of chlorine tabs into the skimmers and ran the pump on recirculate. The water flow seemed very strong and the water level did not change which we thought was an excellent sign of overall health consider its history. After a couple days we put in about 5-6 pounds of DE (whoops too much!) and ran it on filter. The flow is good at first but within a minute or so the water pressure diminishes and after a little while there is zero water flow.

    We did a reset, did several backwash/rinses then dissembled the filter to hose off the filter. Then we made sure the filter was put together correctly and ring on tight, inspected the multiport which was clear, put 3lbs of DE through the skimmers slowly but we have the same symptoms.

    We ran a tiny DE filter on the side of the pool until we get this worked out and that has been clearing the water up.

    At this point we are stumped. The plumbing seems solid since there is no problem with recirculate and there is no obvious issues within the multiport and new filter.

    Any advice guidance or thoughts on this would be greatly appreciated thank you.

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    cowboycasey's Avatar
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    Jul 2013
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    Re: Water pressure low while filtering

    Welcome to TFP

    You have found the best and worst part of a DE filter, they filter great getting every little thing down too 2 microns and that is also what is stopping flow, you will need to backwash when your pressure rises 25% over normal (when you first turned to filter)

    What water test kit are you using, there are 2 available below but I think you will be better served using the TF100 with the XL and speedstir
    Pool: Intex 16x32 15000 gal, 2 speed 340042, Pentair CC320 Filter, CircuPool SJ45 Salt System, Intermatic PE653RC; Hot Tub: 650 Gal SWG Megachlor
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    May 2016
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    Westhampton Beach, NY
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    Re: Water pressure low while filtering

    Quote Originally Posted by cowboycasey View Post
    Welcome to TFP

    You have found the best and worst part of a DE filter, they filter great getting every little thing down too 2 microns and that is also what is stopping flow, you will need to backwash when your pressure rises 25% over normal (when you first turned to filter)

    What water test kit are you using, there are 2 available below but I think you will be better served using the TF100 with the XL and speedstir
    The PSI rises to just above 25psi even after the water pressure falls off. After backwashing and rinsing with a hose the issue repeats immediately and water pressure is lost after 2-3 minutes after filtering starts.

    I'm thinking that this may be an indication of bad plumbing but the high pressure only exists between the pump and filter, is that correct?

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    Pool Tool's Avatar
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    May 2014
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    Western Chicago Area, IL
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    Re: Water pressure low while filtering

    The water pressure doesn't fall off, it raises to 25 psi because the DE filter is catching all the junk in the water. The water flow falls off because the filter is restricting downstream flow into the pool. Unfortunately, like Cowboy said, its normal with that filter type. Your plumbing should be fine and correct the pressure is between the pump and filter. It will be an arduous process getting it cleaned up. Any to vacuum to waste or into a leaf basket with a nylon installed in it to keep from disassembling the filter?
    16' x 32' (21100 gal), vinyl, 1.5 hp Hayward SuperPump,
    Tagelus TA60/60D Sand Filter, Raypak 399K Digital Heater, TF-100

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    May 2016
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    Westhampton Beach, NY
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    Re: Water pressure low while filtering

    Thank you very much for responding. Here is a photo of the pool now. It was dark swamp green when we started with zero visibility.

    Are you saying that once the water stops we need to backwash every 5 minutes? Thanks again!

    Can you clarify "Any to vacuum to waste or into a leaf basket with a nylon installed in it to keep from disassembling the filter?"


    2016-05-24 18.04.51.jpg

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    Re: Water pressure low while filtering

    Before photo
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