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Thread: Filter Size Question

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    Mr. Blue's Avatar
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    May 2013
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    Spring, TX (Houston)
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    Filter Size Question

    New pool owner here.

    I have a Pentair FNS Plus filter, but do not know the filter size. On the side of the filter, there is a chart where the person installing the filter was supposed to 'check off' the model number (see below). As you can see, no one did this.

    The person that was "maintaining" the pool said she was told to add 6 cups of DE after backwashing. Yet, when I look at the filter, the minimum size listed is 36ft, which would call for 8 cups (based on the chart on the bag of DE).

    Is there a way to tell what the filter size is for sure?

    23K Gallon Freeform Tile Inground
    Hayward Super II 1.5 HP -- Pentair FNSP48 DE Filter @ 120 GPM
    Polaris 3900 Sport (with Booster Pump)


    Pool School Attendee -- The TF-100 Test Kit and the Pool Calculator keep my pool Trouble Free -- BBB Supporter

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    Isaac-1's Avatar
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    May 2010
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    Re: Filter Size Question

    DE really should be weighed, using scoops can be WAY OFF depending on how packed the DE is.
    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
    I use and endorse TFtestKits TF-100 from http://tftestkits.net
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    Richard320's Avatar
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    San Dimas, CA (LA County)
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    Re: Filter Size Question

    I had the same problem when I started.

    What I did was measure the height of the grids when I had it opened to clean it. The manual shows different heights for different sizes - all they change is the height of the grids, the center rod, and the top tank. Look at the exploded view on page 9. The parts list shows the grid heights.

    Or, less accurately, measure height of filter. Add height of top tank. That tells you how high you'll need to lift to clear the grids inside. Compare to Table 1 in that link to the manual.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  4. Back To Top    #4
    Mr. Blue's Avatar
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    May 2013
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    Spring, TX (Houston)
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    Re: Filter Size Question

    Quote Originally Posted by Richard320
    I had the same problem when I started.

    What I did was measure the height of the grids when I had it opened to clean it. The manual shows different heights for different sizes - all they change is the height of the grids, the center rod, and the top tank. Look at the exploded view on page 9. The parts list shows the grid heights.

    Or, less accurately, measure height of filter. Add height of top tank. That tells you how high you'll need to lift to clear the grids inside. Compare to Table 1 in that link to the manual.
    Awesome. Thank you!

    I am in the process of deep cleaning the pool. I have taken the filter out and cleaned it once when I first started; I am going to do it again once I am done. I can measure the height of the grids then. Below is what the pool looked like when I started. It is now blue and cloudy...just a little bit further to go!

    23K Gallon Freeform Tile Inground
    Hayward Super II 1.5 HP -- Pentair FNSP48 DE Filter @ 120 GPM
    Polaris 3900 Sport (with Booster Pump)


    Pool School Attendee -- The TF-100 Test Kit and the Pool Calculator keep my pool Trouble Free -- BBB Supporter

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