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Thread: Can I trust this CYA reading?

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    Can I trust this CYA reading?

    I opened my pool about 2 weeks ago and had a bit of a green algae issue, nothing severe but the water was a solid green. I shocked the pool the way I was told (this is pre TFP unfortunately) with the granular type of chlorine. Shortly thereafter I discovered this fine site and switched over to the BBB method. The water is clean but cloudy and has been for a week now. I keep trying to shock but if my CYA reading is correct I know it's not enough. I read in the "turn your green swamp into a sparkling oasis" article not to trust a CYA reading from a murky pool. Just last night I drained about 7" and it's just about refilled now. My CYA reading is 20 ppm HIGHER! I did use about 32 oz of Algaecide 50% (because I had it). It's the alkyl dimethyl benzyl ammonium chloride type. Did that affect it or is the cloudy water reading not to be trusted? The sample from the pool does not appear cloudy however. Here are the last test results:

    pH - 7.2
    TA - 110
    FC - >5 (test kit only goes up to 5 and I just put in 6 gallons of bleach 6%; I know, get the TF100)
    TH - 230?? (kit says add hardness indicator and sample will turn red if hardness present; it turned more like a pale yellow and when I added the titrant it turned a pale blue after 23 drops)
    CYA - 110?? (was 90 before drain/refill)
    Pool size: 30,000 gallons
    Filter: Sand, Triton II TR-100
    Filtration flow rate: 74 gpm
    Pool: IG
    Type: Plaster
    Pump: Emerson, 2HP

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    Re: Can I trust this CYA reading?

    Ask the pool store to check your cya using water only, If they come back with a cya reading then the water is to cloudy to trust a reading.If the reading is zero then your cya is likely too high and I would do a partial drain.
    coloeb,
    20k gal. IG fiberglass/plaster rectangle 32'x16'
    Hayward Superpump 3/4 H.P. primary Hayward model 5060 Booster Pump
    Hayward Pro Series High Rate Sand Filter
    Pentair Model 320 automatic Chlorine/bromine in-line feeder

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    Re: Can I trust this CYA reading?

    I'm not sure that I completely understand the first sentence.
    Pool size: 30,000 gallons
    Filter: Sand, Triton II TR-100
    Filtration flow rate: 74 gpm
    Pool: IG
    Type: Plaster
    Pump: Emerson, 2HP

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    Re: Can I trust this CYA reading?

    He means, do a CYA test without adding any reagent, and see if there's any obvious cloudiness. That would interfere with the test, make it read higher.

    Test results in the >=100 range are kind of unreliable anyway. Could be much higher. After you get your own test kit you can try diluting the sample to see what the level is really.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Can I trust this CYA reading?

    I do have a drop test kit. The pool water by itself for the CYA test showed no visible cloudiness. I don't understand why my CYA went from 90 to over 100 (tube stops at 100, I'm guessing it's 110) after I drained 7" and refilled with well water. For good measure I tested my well water and not too surprisingly there is no CYA present. As I said earlier, I added about 32oz of a Algaecide 50%. Does that add to CYA too? The only other thing I added would be the 9lbs of tri-chlor shock but that was a week ago and before I read up on its side effects.
    Pool size: 30,000 gallons
    Filter: Sand, Triton II TR-100
    Filtration flow rate: 74 gpm
    Pool: IG
    Type: Plaster
    Pump: Emerson, 2HP

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    Re: Can I trust this CYA reading?

    vagrowr,

    You have a lot of things that need correcting so let me address just one of them to get you started....CYA.

    The CYA test is simply not accurate at or above 100. That you drained 7" is not that much and it simply means you are in a range where your CYA is still too high to be measured within the accuracy of the test (+-10ppm).

    Whether through one drain/refill of 50% or multiple drain/refills of a smaller amount, you need to continue to drain your pool until you can dependably measure your CYA at or around 50ppm. You will constantly be struggling if you try to manage that pool with it's current CYA.

    Once you get CYA adjusted down to 50 or less, it will be much easier to manage your FC, which should be your next project.

    We'll help and advise you all the way to balanced water but I think you would get a much more thorough understanding of your pool if you took it one step at a time.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Can I trust this CYA reading?

    Ok, I'll start the drain/refill process at a more significant level but I still don't get why my CYA went up after the drain/refill, even it was a small one.
    Pool size: 30,000 gallons
    Filter: Sand, Triton II TR-100
    Filtration flow rate: 74 gpm
    Pool: IG
    Type: Plaster
    Pump: Emerson, 2HP

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    Re: Can I trust this CYA reading?

    The CYA test is simply not accurate at or above 100.
    Happens all the time.....the test loses it's validity when your CYA is that high.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Can I trust this CYA reading?

    Just wanted to revisit this. First, thanks for the help. I did a partial drain/refill and added some calcium. Latest readings:

    pH - 7.5
    TA - 110
    CYA - 90
    TH - 270

    I know the TA and CYA should be lower but the water is crystal clear and my pH is steady. I add one 182oz bottle of bleach every other day and my Cl levels are good. Should I worry about lowering the TA and CYA levels?
    Pool size: 30,000 gallons
    Filter: Sand, Triton II TR-100
    Filtration flow rate: 74 gpm
    Pool: IG
    Type: Plaster
    Pump: Emerson, 2HP

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    JasonLion's Avatar
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    Re: Can I trust this CYA reading?

    There is no need to worry about TA. Having TA around 110 is just fine as long as your PH is behaving.

    CYA around 90 is livable, but it can cause problems. If you get algae, it will be very difficult to kill it all with CYA around 90. As long as you are careful to maintain the appropriate FC level and don't get algae you should be alright. Over time the CYA level should come down slowly.
    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: Can I trust this CYA reading?

    Dilute your pool sample with tap water then test CYA. If you have a water filter or even one of those Brita filter jugs, use water from that. Carefully measure 50-50. Mix it good, then pour that into the CYA mixing bottle and proceed with the test as usual. Double your final reading.

    The CYA test is affected by temperature, so be sure the sample is warm, especially if the dilution water came out of the refrigerator! You could even mix it and leave the bottle in the sun while you vacuum or something. Mix it real good then pour it in. Take a reading, pour it back into the mixing bottle, shake it some more, try again. Do it several times. I do mine on the patio, holding the tube about waist high with my back to the sun. So the tube itself is shaded but the background is bright. If you get the same reading +/-5 three times in a row, that's what I'd call it. Just remember you diluted it, so double the number.
    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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    Ladeda's Avatar
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    Re: Can I trust this CYA reading?

    Thanks Richard!! This information should be on a sticky. I have wasted so much regent redoing this test, always questioning the results. This makes so much sense and saves on regent use.
    25,000 gal IG Liner - Filter Sand Z Brite - Pump 5 HP - TF-100 test Kit

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