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Thread: CYA keeps dropping...

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    crashd0g's Avatar
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    CYA keeps dropping...

    Ok, I have no idea what is going on, but something in my pool is eating CYA for breakfast, lunch, and dinner.

    Here's the full story for my pool. I purchased and moved into the house Dec 1, 2014 (6 months ago). This is the first pool I have owned, so I had no clue what I was doing, what equipment was what, or how any of it worked. I asked our realtor for a reputable pool service person to give us a once over on the pool and teach me how to maintain it. The guy we had come out was very thorough and gave me good information (lined up pretty well with what is taught here). It was a good starting point. He ran a series of tests and let us know the pool had FC=0 and that the CYA=>100 by a lot. On his recommendation I drained about half of the pool and replaced with fresh water, went to his recommended pool store to get some chlorine and regular testing to get the pool ready to swim in. After the first drain and fill session, the CYA came down to about 70, so I was told that was fine.

    The pool is somewhere between 10K-12K gallons. Since that time, I have added about 10lbs of CYA to the pool over two main treatments. My pool is again nearly out of CYA (I've got reagents on order, so I used a test strip this morning that has agreed with my T-100 test and it showed it in the lower end of the 30-50 range).

    Any ideas what would eat CYA that quickly? The stuff I have been using is from Walmart (Clorox Pool and Spa 100% CYA).
    30x13 irregular shape with a 6' dia spa - ~12K gallons. 3' - 5' deep, gunnite construction, built in 2006. AquaCal Heatwave H120 Pool Heat Pump. Pool Pilot Digital SWG (DIG-220). Pentair Compool Lx100. Pentair Whisperflo Pump 2.5 HP 230V 011775. Century Electric B855 2-Horsepower motor. Pentair CC150 cartridge filter. Single skimmer, bottom cleanouts.

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    Mod Squad JVTrain's Avatar
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    Re: CYA keeps dropping...

    How's your water bill?

    The only way you'd be losing CYA is water drain/replacement. Do you have an autofill? You could have a major leak and the autofill is constantly replacing water.

    If you could also post test results from your TF-100 testing, that would be great. Maybe you have some written down before you ran out of reagents?

    There are rare cases where with inadequate FC that CYA is consumed by bacteria but this is almost exclusively seen in cold climate pools over the winter months.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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    Isolated Spa - 345 Gallons

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    crashd0g's Avatar
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    Re: CYA keeps dropping...

    There is no autofill. I don't feel like I add that much water, either (about 1" of water each week).

    The last full set of tests was from back on 4/26: FC=7.5, CC=0, pH=7.5, TA=110, CH=375, CYA=60, Salt 3100, Temp 83, CSI=-.04. I've been watching and testing the FC and pH and keeping them in line. I had just finished bringing the CYA up to 75 back on 4/12, and as you can see it was down to 60 by 4/26. I got busy and didn't get more in the sock, but I have some floating now (I put about 1 lb in at a time).

    Reagents are on order, so I'll have some more in a few days. I know there was someone else here in FL that was also having issues keeping CYA in their pool. I'm just trying to understand why it keeps dropping so quickly.
    30x13 irregular shape with a 6' dia spa - ~12K gallons. 3' - 5' deep, gunnite construction, built in 2006. AquaCal Heatwave H120 Pool Heat Pump. Pool Pilot Digital SWG (DIG-220). Pentair Compool Lx100. Pentair Whisperflo Pump 2.5 HP 230V 011775. Century Electric B855 2-Horsepower motor. Pentair CC150 cartridge filter. Single skimmer, bottom cleanouts.

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    Patrick_B's Avatar
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    Re: CYA keeps dropping...

    With that amount of water replacement loss seems odd, but there is quite a bit of test error margin on Cya turbidity testing. 60/75 isn't huge. But let's see what the new set of tests bring forth.
    TFP Moderator
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    Mod Squad zea3's Avatar
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    Re: CYA keeps dropping...

    If you still are having trouble holding CYA try testing your FC daily and see how much you loose. If you go to 0 within 24 hours get an ammonia test from a place that sells aquarium supplies and get an ammonia test kit. If you are positive for ammonia you will need to slam the pool. If there is no ammonia then try using a different brand of CYA.
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    crashd0g's Avatar
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    Re: CYA keeps dropping...

    With the question having been raised about a pool leak, I looked up a way to attempt to see if there was one. The test I found and decided to use said to put a bucket, or plastic bin, into the pool on a step. Fill it with water so that the water level was the same in as out and wait 24 hours. If the level was noticeably different, you likely have a leak. Right now I'm about 19 hours into the test and there is more than a 1/4" difference. I'm guessing I have a leak somewhere. Now the fun of finding the leak...and having it repaired...sigh.

    Thanks for your help everyone.
    30x13 irregular shape with a 6' dia spa - ~12K gallons. 3' - 5' deep, gunnite construction, built in 2006. AquaCal Heatwave H120 Pool Heat Pump. Pool Pilot Digital SWG (DIG-220). Pentair Compool Lx100. Pentair Whisperflo Pump 2.5 HP 230V 011775. Century Electric B855 2-Horsepower motor. Pentair CC150 cartridge filter. Single skimmer, bottom cleanouts.

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    Patrick_B's Avatar
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    Re: CYA keeps dropping...

    Rats!! Sorry to hear that, but it was suspected. Good luck with it...
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    Mod Squad zea3's Avatar
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    Re: CYA keeps dropping...

    Check your light niche, skimmer opening, return, and main drain. If you can dive down and plug the main drain that would be a good place to start. You can turn off the auto fill and allow the pool to leak until it stops. Once it goes below the light niche you could plug the return and see if it stops.
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