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Thread: High CYA, how often should I need to add Bleach?

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    High CYA, how often should I need to add Bleach?

    Quick history: Last year, out of the blue, pool turned green. I had no idea what I was doing, so I added puck after puck and bag after bag of shock, probably 30lbs of shock at least in total. As you probably can guess, I couldnt get ahead of the algae. I ended up finding TFP and reading tons about BBB and how to kill the algae. I bought a TF1000 and found out my CYA was through the roof, among other things. I drained the pool (11000 gals) almost completely, leaving maybe 1000-1500 gallons in the pool. I filled it back up, followed the procedure of shocking and checking overnight chlorine loss for several days until I believed all the algae was dead. To my dismay, the CYA level still reads higher than the TF1000 can measure, the dot is no longer visible well before I reach the highest ppm graduation on the container. Ive added borates and maintained chlorine level with bleach since then (about 6 mo).
    Fast forward to today:
    Water temp: 65F
    total chlorine: targeting 11ppm (based on CYA 120)
    pH 7.4
    TA 140
    CH 375
    pool is 11000 gals, with pebbletec finish, cartridge filter, heliocol solar, a pool frog with the mineral pack (no longer using chlorine tablets), and a lectro pure magnetic water conditioner.
    Water is clear, no apparent algae growth. Pool water was as cold as 38 degrees for several days over winter (everything should be dead, right?)
    Now, for my questions:
    1) How often I should be expecting to add chlorine? We arent even at full summer temps here in Tucson and I lose several PPM overnight. If i dose the chlorine level to 11ppm, the next day its around 6-8ppm. I realize that with so much CYA I pay a penalty by having to hold my levels higher, but shouldnt all that CYA be helping me keep the chlorine in the pool overnight? With a very high CYA, 120+, how much available chlorine loss should I expect from day to day?
    Is this quick drop in chlorine a symptom of another problem that I haven't read about yet?
    2) Does it seem realistic that I could empty a pool that had a huge (unknown) CYA 85%+ (about 1000 gals left) and refill it with tap water to 11000 total, and still have a CYA of 120+? I'm trying to avoid draining the entire pool again this season, but if the daily chlorine loss from #1 above is so great, I may have to.

    thanks very much for the help - this forum is a fantastic, well beyond the garbage the local pool store has tried to feed me. - andy

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    Mod Squad jblizzle's Avatar
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    Re: High CYA, how often should I need to add Bleach?

    If you are losing more than 1ppm overnight (test after dark and before sun rise) then there is something living in the water ... requiring the shock process.

    Realize that the pH test is inaccurate when the FC > 10ppm.

    Have you done the CYA test using half pool water and half tap water and doubling the reading?

    I would do that and then replace enough water to get the CYA in check.

    Posted from my Droid with Tapatalk ... sorry if my response is short
    Jason, TFP Moderator
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    JasonLion's Avatar
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    Re: High CYA, how often should I need to add Bleach?

    With extremely high CYA levels you should only need to add chlorine every couple of days. The only way you could be losing as much chlorine as you describe is if there is something growing in the water, presumably algae.

    It is possible for CYA to crystalize in the plumbing when CYA levels are exceedingly high and then redissolve later when CYA levels come down. We don't hear of that happening very often, but it is possible.
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    Re: High CYA, how often should I need to add Bleach?

    using the tap water method, it looks like my CYA is slightly higher than 200. the pool calculator says to replace 60% of my water to bring down CYA and 30% of my water to bring down my CH. Is it reasonable in arizona to think that splash out, filter cleaning (I use pressurized pool water to clean my filters to 'drain' more water), and evaporation will help me this summer, or should I just bite the bullet and drain again? GD bags of shock and trichlor tabs!!! *#$*#$&# thanks for the help.

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    Re: High CYA, how often should I need to add Bleach?

    Evaporation does not help at all.
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    Mod Squad jblizzle's Avatar
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    Re: High CYA, how often should I need to add Bleach?

    If the CYA test was still below the 100 mark using 50/50 pool/tap water, then you may be well above 200ppm. You could try it again with 2/3 tap and 1/3 pool water and triple the reading, but would be losing more accuracy.

    The only way to drop the CYA is through removing and replacing water OR reverse osmosis. Where are you located in AZ? It is only available in limited places around the country and PHX is one of them ... although it will run your around $400 I think.

    Evaporation will not lower the CYA levels. There is no way that splash out and filter cleaning is going to replace 75% of your water ... and before that happens, it is going to be very difficult to get and keep your pool clear.

    Not sure why you said the calculator suggested 60% replacement, that would only drop you from 200 to 80ppm which is still too high (unless you were going to have a SWG).
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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