1. CYA overdose?

Hello pool gurus! I have a new pool, and discovered Pool School a few days ago. Until coming to school, I was using a couple of 1" trichlor tablets in the built in chlorinator inside the filter every couple of days (for a total of 15 tablets, I think). I was using HTH 6-way test strips, and never getting any FC registered. I stopped using trichlor tabs and started using 8.25% bleach, lots of it. My chlorine disappeared promptly after the sun came up. The test strips were showing me a CYA of about 30-50, but after I calculated how much CYA I would have gotten from the 15 1" tabs I had already used, I realized the CYA couldn't be more than about 8ppm?

So, after a trip to purchase the needed chemicals, I used PoolMath to calculate how much CYA I needed to add. I used a target of 60ppm of cya because I had read that in my desert climate I might need that much. By yesterday I had acquired the FAS DPD drop test kit and my cya test didn't register any cya. I asked PoolMath to calculate what I needed to raise the cya from 8ppm to 60ppm and got a response of 40 ounces by volume of 100% cya. Last night I measured out 5 cups of the cya and put it in a sock and placed it in front of my return jet, and massaged the sock so that most of the powder came out fairly quickly, then left the rest on it's own and the sock was empty this a.m. I also added about 40 oz of 8.25 bleach, about 9 p.m.

At 10:30 this am after the sun had been out for many hours, I was delighted to find, with a quick dip of a test strip, about 3-5ppm of FC. At about 12:30 pm, same thing. So at 4:30 pm I got out the good test kit and measured FC at 3.5ppm, doing both the 10ml and 25ml sample tests, and getting same result with both tests. With CC at zero. Very good, yes?

Ok, so then I measured TA (275=high) and then PH, which I was surprised to find had decreased from previous high of about 8.0 or more to between 7.6 and 7.8 (acid demand was only 2 drops to 7.4, and 5 drops to 7.2). I have on hand sodium bisulfate 93.2 to adjust ph but haven't done so yet.

Because I was having so much fun with the test kit, I decided to measure cya even though I had read not to bother for about a week. Ummm, I was very surprised to get a reading of over 100. So now I wonder what I did wrong? Did I measure the dry acid correctly? I used my kitchen measuring cup, filled it to 16 oz twice and then to 8 oz, 40 oz all together. Is that correct? Or did I use the Poolmath calculator incorrectly? Is there some way the test could be wrong? Also, if I'm getting that reading now, less than 24 hours after adding the cya, will it be through the roof in a week?

What am I missing? I know it's not an emergency, but I'd like to know if there's something I did wrong or what could have happened?

Also, I'd like to ask what target I should use when I adjust the PH? And should I wait until I know that all the cya is dissolved? And is the evening the best time to top off the chlorine, and what should be my target for FC; should I go a little high because of my climate (and apparent high cya?).

Thanks in advance for any help!

2. Re: CYA overdose?

A few things... First, you may have simply gotten a CYA-heavy sample because it is not fully dissolved and distributed...especially if you took the water sample from near the return it is hanging on. Second, this is why it is common advice not to do major changes in one pass; you probably should have added enough CYA to reach a target of 40 and then tested to be sure. That way you know for sure that things (like your pool volume number) are right and you don't overshoot.

I would target ~6ppm FC based on your original intention to hit 60 CYA. You can always adjust later when the CYA is fully distributed. For PH, if it is between 7.2 and 7.8, I would probably leave it for now. You don't want to use a ton of chems especially if you end up having to dump some water because you went way over on CYA.

3. Re: CYA overdose?

The test strips were showing me a CYA of about 30-50, but after I calculated how much CYA I would have gotten from the 15 1" tabs I had already used, I realized the CYA couldn't be more than about 8ppm?
What am I missing? I know it's not an emergency, but I'd like to know if there's something I did wrong or what could have happened?
I suggest you recheck PoolMath on the tabs.

4. Re: CYA overdose?

Did you remember to change the volume of your pool at the top of the pool calculator? Did you account for the fact that the pool is not filled to the top of the liner? (A 48" pool is usually actually filled to 42-44") those are some of the things that could affect your numbers.

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