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Thread: Why is my CYA still at 100

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    Join Date
    May 2014
    Altadena, CA

    Why is my CYA still at 100

    I'm a new owner of a 1950'ish ~22,000 "in" ground pool. My family and I don't live there yet because we are about to renovate. We are about 15 minutes away and check on the house about once a week. Several weeks ago it got warm and turned green over the work week. I went to Leslie's, purchased a three step shock and clean products, which worked. Last week, it turned green again. I searched and found this site and read about CYA and chlorine pucks, which I was using and I'm sure the previous owner was using. So, when I tested the CYA levels, using the black dot in the test tube, it was above 100. Using the calculator on this site I drained the pool approx. 60%, which took about two days, filled it back up, and have been keeping the chlorine at shock levels using liquid chlorine or bleach from the grocery store. I'm doing this the best I can with work and not being able to live there, but it is sparkling now. However, I checked and the CYA was at 100. My wife took a sample to Leslie's and they too said it was around 100. Yet, they said 100 is normal around here and I'm fine. I thought I wanted my CYA around 50? I also thought draining the pool 60% would have brought that level down a lot?

    Why would the CYA levels still be that high after a drain?

    Is a 100 level ok? If yes, how much liquid chlorine should I expect to use a week? Will I be able to test and dump on weekends?

    I live in Altadena, CA and we are in a record drought, so I already feel bad about filling the pool. I am thinking of waiting until this winter (rainy season) to drain the pool again.


  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Why is my CYA still at 100

    Welcome to TFP!

    You said the CYA was above 100 when you first tested. It is a logarithmic scale, so likely it was over 200 and now you have replaced half the water so the cya dropped by half. You should really do another 50% drain.

    So how did you determine the correct FC level to SLAM the pool if you did not know the CYA? As it is now, you would have to maintain the FC around 40ppm to SLAM ... that is why you should replace water.

    What test kit are you using?
    Jason, TFP Moderator
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  3. Back To Top    #3
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Why is my CYA still at 100

    The short answer is, the spacing on the CYA tube is not equidistant. The difference between 90 and 100 is hardly anything. Above 100, the lines would get so close together they'd all melt into each other. Too bad you didn't find us first, we could have explained it and pointed you to the extended test kit directions, where you would have gotten a more accurate reading.

    Your pool turned green because you had inadequate free chlorine for your stabilizer. Here's something I wrote last year. It should sound familiar. Actually, where we live, it gets worse, because we maintain our pools all year long.

    We'll take a 16000 gallon pool, because that's what I have. On a fresh fill, prominent national pool chain recommends 2.5 pounds pf stabilizer per 10,000 gallons, which works out nicely to 4 pounds which brings CYA to 30.

    With an average loss of 2 PPM/Day or 14 ppm/week, I'll have added 8.6 PPM/CYA if I used trichlor pucks perfectly. And they recommend a weekly "shock" of dichlor between 5 and 10 FC.... 2-3 oz per 10,000 gallons. Split the difference; I'll add 4 oz. CYA went up another .9. the end of week one, I have added 9.5 more CYA. It is now 39.5. Mimimum FC for that is 3, so I'm probably okay.

    Week two, up to 49 CYA.
    Week three, 58.5. Minimum FC should be 5, but they recommend 3 as ideal, so the pool looks a bit hazy. So I'll toss in a little extra dichlor "shock" to jack FC up to 10. Which adds another 6.4 CYA. Keeping count? We're up to 64.9 now.

    That caught the algae just in time.. we had two weeks of good luck. A steady diet of pucks and 4 oz. "shock" each week only added another 19, up to 73.9 now.

    Week 6 it started looking funky, so we "shocked"it once again. CYA is up to 99.3. But minimum FC to keep algae at bay is 8, and we're still holding things to 3, because prominent national chain's preprinted sheet shows that as ideal. So algae got a toehold and the pool has a bit of a tint. So we throw two whole bags of dichlor in which jacks it another 7.6 by the time week 7 is over, we're at 116.4, because we had pucks in the floater the whole time. 7 weeks, from 30 to 116.4. Let's say there are no more algae outbreaks because they sold me a huge bucket of phos-free and another of yellow-out monopersulfate "shock" Nothing but the pucks and the extra 4 oz of dichlor "shock" weekly. So the next 7 weeks added 66.5, which brings the total to 182.9 CYA.

    Now if we didn't understand this and things looked a bit hazy, we might throw an extra puck or two in the floater every couple weeks, which will drive it over 200 easily.

    If the pool truly is algae-free, it is possible to maintain it. I've done it, with CYA somewhere north of 220, and water restrictions in place. But it's not easy and I don't recommend it. It does require a FAS-DPD chlorine tester. They are hard to find in stores.
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  4. Back To Top    #4
    Isaac-1's Avatar
    Join Date
    May 2010
    SW Louisiana

    Re: Why is my CYA still at 100

    Sure a CYA of 100 is great for Leslies, it means you will be fighting algae outbreaks all summer and they can sell you hundreds or maybe even thousands of dollars worth of chemicals all to fight something caused by following their advice to begin with.
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  5. Back To Top    #5

    Re: Why is my CYA still at 100

    I managed my pool with a CYA level of 90. It was more expensive to keep my FC at 7ppm but I made it through the summer without getting algae. We had a ton of rain during match and April of this year so fortunately there was enough spillover to lower my CYA to 60. Anyway I totally recommend another partial drain especially since you can't dose the water with chlorine every day, but it's possible to limp along with high cya.
    17,000 inground gunite pool finished June 2013. Pentair variable speed something or another. Polaris cleaner, inline rainbow chlorinator. Using trichlor until CYA reaches 50-60.

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