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Thread: Does low speed filter better than hi speed?

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    Does low speed filter better than hi speed?

    Having a 2 speed motor (which I might have to replace), besides the advantage of energy savings, it has been touted that lower speeds actually filter better, trapping smaller particles that might get shot out by the higher speeds. In your experience, do you believe it's true?
    20 x 40 Inground vinyl pool (24000 gal)
    Hayward SuperPump with dual speed AO Smith STS1152R Motor

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    frustratedpoolmom's Avatar
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    Re: Does low speed filter better than hi speed?

    What kind of filter do you have?

    I run my filter on low 24/7 and have had zero filtration issues...and a very reasonable utility bill.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: Does low speed filter better than hi speed?

    I cannot answer for pool filters, but in fish tanks we recognized that there are two sorts of filtration; biological and mechanical (the third, chemical filtration, being not really important in fish tanks). If you were relying on mechanical filtration, then high flow rate was best, so you got the most water past the filter in a given time. If you were relying on biological filtration, then you wanted a slower rate, or a larger diameter of filter, so that the bacteria responsible for processing the wastes had time to work.

    I don't know if that translates to pool filters at all, but I am pretty sure that a cartridge filter is mechanical filtration, so more flow is good. I don't know if a sand filter is biological filtration, it would be in a pond, where sand filters can be used, but I dont' really understand the mechanism of if that would mean that slow throughput would be good. I guess chlorine is actually chemical filtration.... and that would seem to be independant of flow rate through the filter, as long as you maintain good circulation to keep the chlorine moving into the places where it is needed.

    Which is to say, I don't know but I am interested in the answer.

    Anona, still a novice
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Lershac's Avatar
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    Re: Does low speed filter better than hi speed?

    Well biological filtration in a pool is a big no. The chlorine in pools will kill off any biological filtration that would ever set up housekeeping in a filter system. Sand, Cartridge and DE are all mechanical filters, running water through porous filters to trap the particles so they do not return to the pool.
    (DIY):16K Gal 20X30 rectangular IG Gunite, w/spa, CCP 520 filter,2 Pentair VS pumps, 400KBTU Pentair gas heater, Heat Pump for cooling, **update5.25.2013** added an intellichem with acid pump that will control existing SWG. My Build Thread Here

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    Cherie's Avatar
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    Re: Does low speed filter better than hi speed?

    We're with FPM. We run our 2-speed on low 24/7 with absolutely no problem.
    32x16 buried Doughboy, 4' shallow - 7' deep
    Pentair Dynamo 1 hp, 2-speed - Pentair 150# SD40 w/zeolite (75#)
    One skimmer/two returns/Aquabot Turbo T2

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    JasonLion's Avatar
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    Re: Does low speed filter better than hi speed?

    All of the filter types filter better at lower flow rates. At higher flow rates there is more water pressure trying to push the dirt through, so more dirt gets through. The difference isn't huge, but it is noticeable.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Does low speed filter better than hi speed?

    The slower the water goes through a sandfilter the better, this is part of the reason why commercial tanks are so big (not just fiction losses and bigger pumps/pools) but their recommended flow rate is a lot slower than a domestic pool (gpm/squarefoot filter)

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    Re: Does low speed filter better than hi speed?

    Quote Originally Posted by anonapersona
    I cannot answer for pool filters, but in fish tanks we recognized that there are two sorts of filtration; biological and mechanical (the third, chemical filtration, being not really important in fish tanks). If you were relying on mechanical filtration, then high flow rate was best, so you got the most water past the filter in a given time. If you were relying on biological filtration, then you wanted a slower rate, or a larger diameter of filter, so that the bacteria responsible for processing the wastes had time to work.
    Not quite accurate. Been keeping freshwater and salt/reef tanks since the early 60's (had my first fresheateraquarium when I was 6! and kept freshwater through high school.) Been keeping exclusively salt since the mid 70's and have kept tanks from 2 gal to 150 gal (at the height of my insanity I had 9 reef and invertebrate tanks in my house when I lived in Miami!) so I have experimented with many types of filters, both bought and home brewed.

    Quote Originally Posted by Aquaclear-NZ
    The slower the water goes through a sandfilter the better, this is part of the reason why commercial tanks are so big (not just fiction losses and bigger pumps/pools) but their recommended flow rate is a lot slower than a domestic pool (gpm/squarefoot filter)
    This is also true of aquarium filtration. FWIW Pentair sells EXACTLY the same sand filters for pool and large aquairum/pond usage under different names. jAquairums also use slow sand filters for mechaical filtration and the slower the rate, the better the filtration. High flow rates are more likely to push dirt particles through the filter media.

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