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Thread: How much to worry about CSI after pool wtr reverse osmosis?

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    MattM's Avatar
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    How much to worry about CSI after pool wtr reverse osmosis?

    Calcium in our pool reached our high threshold point earlier this month and we had reverse osmosis service performed to bring it down. And, yes, it brought nearly everything else down as well.

    PH dropped to 6.8, TA dropped from 120->50, Borates went to almost zero, salt to 800, CYA to under 10, calcium to slightly under 100. Luckily, I had planned ahead and had replacement supplies on hand.

    The RO service took about 17hrs and afterwards our CSI was briefly about -1.6. I got the borates in rather quickly to raise TA and PH, and then brought down CSI back into the -0.35 to -0.50 range over about 36hrs. Salt is back to 3400 and all appears to be running fine. The pool has stayed in the low CSI range for the last week - I was hoping warmer weather would help get it back above -0.30 but it may take another week or two to know if we get sustained higher temps. Due to our intellichem, the highest sustained PH I can keep is ~7.65.

    Should I just wait or add a small amount of calcium to the pool water now, or how long can I reasonably wait with CSI this low? We have a pebble sheen finish that we try to be careful of. CH is currently 125 and I can see bringing it up to 150-160. Normally, CH increases by 10 pts during each winter month, and 15-30 pts during summer months.
    24K gallon inground gunite/pebble sheen pool, 34'x16' 4-7.5ft deep, 750sq ft solar, pentair ultratemp, intelliflow vs+, ic60, intellichem w/ acid pump, quad de 100, intellibright 5g, intellitouch i5-3s with Screenlogic2, 3" primary piping - 2.5" at equip pad, auto switched deep heating and main returns, automatic safety cover w/ electronic lock and embedded recessed undertrack, sealed stamped concrete deck, dolphin deluxe 5, started up December 2011.

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    JasonLion's Avatar
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    Re: How much to worry about CSI after pool wtr reverse osmos

    CSI at -1.6 is only alright for very short periods. CSI at -0.5 is fine for quite some time, if not forever.
    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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    Richard320's Avatar
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    Re: How much to worry about CSI after pool wtr reverse osmos

    You're in the safe zone, so don't worry.

    Also, do not freak out if CH climbs a little even if you haven't added any water. If you have any scaly patches, they may start dissolving, which will raise CH. It doesn't mean it's leeching it out of the plaster.
    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!

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    MattM's Avatar
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    Re: How much to worry about CSI after pool wtr reverse osmos

    K, I had been keeping CSI in a tight zone between 0 and -0.2 ever since the pool was first started up...glad to hear that -0.5 should be safe enough until the water temp increases. That is a lot of stress off my shoulders.

    In any case, I wouldn't think that I'd have any scale to dissolve given that the csi had always been kept slightly negative....but there was the jump from 100 to 125 during the last week, but hopefully it is holding steady now.
    24K gallon inground gunite/pebble sheen pool, 34'x16' 4-7.5ft deep, 750sq ft solar, pentair ultratemp, intelliflow vs+, ic60, intellichem w/ acid pump, quad de 100, intellibright 5g, intellitouch i5-3s with Screenlogic2, 3" primary piping - 2.5" at equip pad, auto switched deep heating and main returns, automatic safety cover w/ electronic lock and embedded recessed undertrack, sealed stamped concrete deck, dolphin deluxe 5, started up December 2011.

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