What happened to my FC?

[Galun]

I have to admit that I test my pool sporadically, and so I am at a loss with my test results. All tests are done with tftest kit.

This past saturday I tested the pool with the 5 drop quick test, and it was clear. Uh oh. I poured in a 182oz of 6% bleach, which according to pool calc will bring FC from 0 to about 5 in my 20k gallon pool. Water looked clear.

Sunday we had a pool party. Everybody had a great time. Nobody got itchy eyes so no CC I suppose?

Today I tested again with the 5 drop test. Clear again. Uh oh. I am now thinking my automated chlorinator may be broken, so I poured in another 182oz bottle of bleach. Then I thought maybe the chemicals went bad? I went back to the pool to get another water sample - this time right around the area where I poured in the bleach. Did the test and it was still clear. Then I used the fas dpd drop test. The water didn't turn pink. Huh? That was water right at where I poured in fresh bleach. Then I decided to take a sample of 6% bleach directly from the bottle and test that. It should turn pink after I add the powder right? Nope, it stayed clear.

I checked the chlorinator as well, and the bleach level had been going down. So I think it's pumping bleach into the pool.

So... Any suggestions here? Do I have no FC in the pool or did my chemicals turn bad? Or maybe the bleach I got at Costco is really really really old?

 

[Isaac-1]

My guess is amonia in the pool, kids pee (verb or noun), amonia will very quickly react with chlorine and they will neutralize each other out. You need to keep adding chlorine until it maintains at the correct level for your CYA level, then do an OCLT (overnight chlorine loss test) to check if anything is growing in the pool that you may need to shock (process not product) for.

Ike

p.s. the test from the 6% bottle would not work, I think because you would have to add an insane amount of 870 powder for it to show. Sure you could have bottle over water instead of 6%, but more likely was saturated and bleached out by the bleach. the OTO test is the best one when you expect insanely high levels of chlorine, you could try it with a sample from the bottle diluted say 20:1 with non chlorine water, if you get a burnt orange instead of yellow it is a sign of insanely high chlorine levels.

 

[Galun]

My guess is amonia in the pool, kids pee (verb or noun), amonia will very quickly react with chlorine and they will neutralize each other out. You need to keep adding chlorine until it maintains at the correct level for your CYA level, then do an OCLT (overnight chlorine loss test) to check if anything is growing in the pool that you may need to shock (process not product) for.

Ike

But I tested bleach straight from a fresh bottle. It's still clear in the 5 drop quick test and the fas dpd test after adding powder...

 

[Isaac-1]

read my ps, try the 6% diluted down about 20 to 1 with non chlorinated water in the OTO color match yellow test

Ike

p.s. is your 5 drop test OTO or DPD, one advantage of OTO is it does not bleach out at high chlorine levels like DPD does, this makes OTO a god indicator of presense of high levels of chlorine, even if it is not as good at telling the exact amount

 

[Siamese]

Galun - Have you tested your CYA level? This reminds me of the issue I had last year when I opened my pool and couldn't hold an FC level. Here's the post.

opening-pool-can-t-get-fc-above-1-t32857.html

It turned out that my CYA had turned to ammonia over the winter and there was a huge chlorine demand. It took dozens of gallons of bleach to resolve the problem. I was where you were, thinking that the bleach had gone bad and that my test kit didn't work. Turns out it was ammonia to blame.

 

[Bama Rambler]

If you're on chlorinated public water run a test on a sample of it. That should tell you if the reagents are good.

If that works and it's the OTO test, take a gallon of pool water and put a tsp of bleach in it and test it immediately. If it shows no TC take a gallon of tap water and add a tsp of bleach to it and test it. It should be really orange. If the pool water sample is clear but the tap water shows a lot of chlorine, I agree with the ammonia test.

 

[Galun]

Thanks for pointing me to the CYA to ammonia problem. I tested CYA and I have 0-20. Last I tested about a month ago, it was at 30.

Turns out the chemicals are fine. I did not dilute the bleach and thus there was no pink from the fas dpd test.

Here are my observations.
1). Last night measured FC at 4, CC at <0.5.
2). This morning measured FC at 4, CC at <0.5. (so I guess I don't have stuff growing).
3). This evening measured FC at 0.5. The day had full sun and my pool was covered with a bubble cover. This loss was way higher than what it was before (about 1 FC drop per day).
4). CYA is 0-20. I can still see the dot when the tube was full.

I think I have no or little CYA in the water, and that's why my FC is dropping so much during the day. However, I don't think I have an ammonia problem, because my FC didn't drop overnight. From what I see, people with ammonia problem seem to lose the FC very quickly, measured in minutes / hours. But my FC held overnight... That should mean no ammonia problem? Hopefully it's just lack of CYA to protect the FC from the sun that's causing my lack of FC.

I have now lowered my ph to 7.2 and brought the pool to a target of 12 FC, which is shock level at 30 CYA. Later on tonight I will add some instant conditioner to the pool to try to bring the pool to 30 CYA. If my FC holds again overnight, then I don't think I have stuff growing in the pool or an ammonia problem.

Any other suggestions will be much appreciated. Thanks!

 

[Bama Rambler]

I agree, you don't have ammonia.

Do you have an autofill that may be masking a leak? That would explain the CYA going down.


You need some CYA in the pool. I'd start with about 40 ppm and see how that works for you.

 

[Butterfly]

Did you turn off the chlorinator for the OCLT?

 

[Galun]

Thanks for the suggestions. I will get some instant conditioner today to get CYA up. Last night I poured in whatever I have left into the pool. By the bottle instructions it would be about 8ppm. In the CYA test it did get more cloudy, but I can still see the dot even at the 20ppm line. I will shoot for 30 CYA with instant conditioner and use pucks for a while to get more CYA into the pool. I also plan on maintaining shock level over night - might as well do a deep clean of the pool while I am at it.

I had actually asked about losing CYA here before. I don't have an autofill. I do lose water very slowly but that may just be evaporation.

Butterfly - I did not turn of the chlorinator, but it's a pump that pumps bleach for an hour in the afternoon. It would not have affected the OCLT.