CYA addition not resulting in predicted ppm increase

[PhillipH]

With my new TF-100 test kit, I had been measuring CYA at 40-50ppm. I actually feel pretty confident in my ability to perform this test. I'll perform it 2-3 times in a row and always get the same exact result. I'm also getting consistent results from day to day and week to week. So, I wanted to get my CYA up to the 70-80 range that is recommended by TFP and by my SWG manufacturer. I recently added 4 lbs of CYA, and the pool calc says this will add 20ppm for my 25k-gal pool. However, I'm still reading about 50ppm. I added the first 2 lbs by dissolving in a bucket and painstakingly pouring the dissolved slurry into the water, then refilling and letting the remaining portion dissolve some more. 1/2 day. I then added the last 2 lbs by putting it in a sock in the skimmer. That took every bit of a week to fully dissolve (8 days). It's been about 5 days since the contents of the sock fully dissolved.

Why is my CYA not measuring higher?

I know that most people at TFP don't think very highly of pool store employees, but I should add that my PS guy said that you can sometimes add and add and add, and you might find it impossible to get CYA up near 80ppm or over. I'd never heard that before. Is there anything to that?

Thanks.

 

[rastoma]

but I should add that my PS guy said that you can sometimes add and add and add, and you might find it impossible to get CYA up near 80ppm or over. I'd never heard that before. Is there anything to that?

Thanks.

I'm definitely not an expert around here but I've read just about every post here I think LOL I've never heard that before. I don't think that's true. Because people that use pucks that have CYA in them, can end up with CYA levels of 200+

Have you backwashed recently?

Do you have an automatic water leveler? If so, you could have a leak and the leveler keeps the water up so you don't notice it.

 

[257WbyMag]

Are you certain about the volume of your pool?

I'd wait a few days and test your water again. If there is no change in your value, then go ahead and add some more CYA to get you where you need to be. You certainly can get the level to 80 ppm and far beyond it. In fact, we see those posts almost every day here.

 

[duraleigh]

the pool calc says this will add 20ppm for my 25k-gal pool

What is the dosage rate on the side of the box?

 

[JasonLion]

Just to add to the possibilities, about two years ago there was a whole batch of CYA, sold under several different brand names, that didn't actually contain any CYA. I haven't heard of that happening again, but it is possible.

 

[Richard320]

Why is my CYA not measuring higher?

Is the water cold? I've gained 20 ppm just by letting the water warm up, leaving the bottle on the table in the sun a while.

I know that most people at TFP don't think very highly of pool store employees, but I should add that my PS guy said that you can sometimes add and add and add, and you might find it impossible to get CYA up near 80ppm or over. I'd never heard that before. Is there anything to that?

Thanks.

C'mon over to my house and I'll show you what a CYA test of 140 looks like. It was 220, but a backflush, pumping out and diverting a gutter downspout to refill it during rainstorms has reduced it somewhat. That's from pucks. The previous homeowner and the pool service liked to buy huge pails of pucks, and keep 4 or so in the floater year-round. I've still got an empty bucket floating around in the shed somewhere....

 

[PhillipH]

Thanks for the replies. I'll answer all questions below.

No auto water leveler, and no backwashing b/c I have a cartridge filter.

I'm pretty certain that my pool is 25k-gal or close. That's from the local company who built the pool.

Dosage rate: well, it gave a rate to use for start-up, then it gave what they called a maintenance dose -- add x amt every month. I know we at the TFP don't do that with our CYA, so the label wasn't helpful. (The label did say "100% cyanuric acid".) I went by the pool calc, and based on my volume of water, I knew I could safely add the entire 4 lbs without going over 80ppm. I wanted to give that plenty of time and see what it brought the CYA up to, then reassess and see if I needed to add more.

I like Jason's suggestion the best. lol. That's what it seems like!

I went ahead and bought more CYA yesterday and put 3 lbs in a sock in the skimmer. Unfortunately, it's the same brand from the same store, so we'll soon know more about Jason's idea. If 7 lbs doesn't move it, there's your answer.

My water has been above 70 for at least 6 weeks, and it's been consistently above 75 for probably 4 weeks. The last couple of weeks, it's ranged from about 77 to 82. Mostly around 80.

When doing the CYA measurement, I try to follow the TF-100 instructions closely. I shake the mixture well, then let it sit for at least 30 seconds, then shake again, then pour into the view tube. I have alot more trouble doing the pH colormetric matching in the 7.6 to 8.0 range than I do knowing when the black dot disappears. I feel pretty confident of knowing when to "call it", and I think I'm doing it very consistently. Maybe I'm not, but it seems like I'm doing it correctly. I've already been directed to the Taylor webpage showing the 3 pics of the disappearing black dot.

Thanks again,
Phillip

 

[ac130loadmaster]

I am definitely not an expert! But from doing some reading by the pro's on here I have heard that it sometimes takes a week to see the increase register on a test. So I would add the appropriate amounts of CYA according to the pool calc and wait a week to see where the level balances at. I would rather add more CYA if needed than to have to drain my pool because I put way to much in it.