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Thread: Recommended Backwash Flow Rates - Where is my sand?

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    wpbucher's Avatar
    Join Date
    Feb 2012
    South-Central Pennsylvania

    Recommended Backwash Flow Rates - Where is my sand?


    Just before opening pool for the season, I muscled off the top of my Triton T100 sand filter. The manual states that there should be 11.25 inches between the top of the sand and the top of the filter. For some reason they call it: " 'X' FREE BOARD". I had a gap of about 16.5 inches.

    I added 150 pounds of pool sand to make the gap 11.25 inches. NOTE: Per the manual, the T100 only holds 450 pounds of sand.

    So I wondered, where did my sand go? Possible answers:

    1. The PB did not fill sand filter...put in 300 pounds of sand instead of 450 pounds.
    2. The sand was lost to waste when backwashing.

    In the troubleshooting part of the manual the the solution to "sand lost to waste" is to decrease backwash flow.

    I checked my Pentair VF pump and backwash was set to 60 gpm for 2 minutes and rinse for 1 minute.

    I saw on another thread on TFP where a person posted that the backwash rate should be 15 to 20 gpm per sq ft of filter area.
    The T100 provides 4.91 sf of surface area.

    Thus....if I did the math correctly....I should be backwashing at a rate of 75 to 95 gpm

    Thus, my conundrum.... It appears that 60 gpm is too low a backwash rate....but if I'm losing sand to backwash....I don't want to increase the backwash rate.

    Should I keep the backflow at 60....or increase to 75 or 85 gpm?

    Your thoughts and suggestions are appreciated.

    NOTE: Getting top off was a bear. I cleaned the grooves with a toothbrush and applied Magic Lube liberally...hopefully the next removal will not require as much torque.

    PS: I am amazed and astounded that Pentair can put out an 84 page owners manual for the sand filter and never state the recommended backwash rate.
    2013 HotSpring Grandee with Ace Sanitizing System
    25K IG vinyl pool with Alps spillover spa and waterfall. Build Date: June 2013
    Triton II TR100 Sand Filter, Pentair Master Temp 400 natural gas pool heater, Intellichlor SWG, Rainbow Chlorine Feeder
    Pentair VF filter pump, WhisperFlo 2 hp WFE-8 waterfall pump, WhisperFloFX 2 hp spillover spa pump
    Intellibrite 5G (2 pool and 1 in spa) lights :: TFT-100 test kit, Taylor K-1776 test kit

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Recommended Backwash Flow Rates - Where is my sand?

    15 GPM/sqft is a good backwash rate for sand filters. Lower backwash rates often work tolerably well though they are less dependable, and you should be able to go a fair bit higher than that without problems.

    It is extremely unlikely that you were losing any significant amount of sand due to backwashing. I suspect that they simply didn't fill it full enough.
    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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