where is my CYA disappearing to?

[aylad]

There are bacteria that can break down your CYA and lower it--but that usually happens when the pool is allowed to turn into a green swamp. It is almost impossible to explain a drop in CYA from 30+ to zero overnight--except maybe by testing method. Who is doing your testing? And has the person doing the testing using the same method with the same lighting each time? Was a different vial of reagent being used? When the test showed zero, was the sample and reagent shaken well, then allowed to sit for a few minutes before being poured into the vial, or was it immediately poured in? All of these things can skew what is already a very subjective test, so I would rule out testing problems before looking for a problem with your pool.

Also, when you added your CYA, did you add it via skimmer, broadcast it into the pool, or put it in a sock in front of a return? If it went in through the skimmer, and you cleaned/backwashed the filter less than 4-5 days after adding it, then you may have washed it out. Four pounds of CYA in a pool your size should have raised your CYA way higher than 30.

Janet

[Watermom]

I think you are off on your pool's volume. I have a 24ft AG and my volume is somewhere between 12 - 13,000 gallons.

[CarlD]

Are you testing your CYA with strips? Even the two best--Hache and LaMotte are pretty worthless on that test--you cannot tell if your CYA is 0 or 50! I know, I've used them. I MAINLY use them to check if my chlorine is there or not, but I look at the others and try to figure them out. Frankly, the ONLY way to measure CYA is with the black-dot test tube.

[dalejanus]

As usual, one can never be too clear when posting to a forum. My apologies.

My 24 ft AG 4 ft high so that makes it 12,000 not 10,000. Don't know what I was thinking there...

The cya did not disappear overnight, it was probably about 1 week between tests. We did have some rain, but it only added a few inches, if that.

I have the Taylor test kit I got new this year and do it outside in the evenings. Based on Ben's kit instructions, I wait at least 30 seconds after mixing before testing, but I see that I should wait longer. I like the idea of mixing cya first, then testing everything else, then looking for the black spot.

I have already gone through 1 bottle of taylor cya reagent so I will order a large refill bottle.

When I add CYA I use a sock in front of the return and it takes about 1 day to dissolve a 1 or 2 pound bag/bottle. I can't remember the size, I'll have to pay more attention.

We are not a green swamp, the water is clear. But yesterday, we could see some algae trying to get started on the bottom. We vacuumed and backwashed.

---Dale

[aylad]

Try mixing the pool water and reagent first, and let it sit 2-3 minutes before testing again, and see if that makes a difference. Honestly, if you are losing that much over a week's period of time and can't account for it with dilution, you might start investigating a possible leak.

If you have algae starting in the pool, you need to shock the pool and maintain that shock level until the algae is gone. Vacuuming and backwashing may get rid of what you can see, but it won't get rid of the algae that's still in the pool that is too small to be visible.

Janet

[Watermom]

OK. Now your volume makes more sense. In the first post, you stated 28ft AG with 10,000 gallons. That is why I asked.

[dalejanus]

ok, more detective work tonight.

I take a sample to the pool store and they tell me I have cya of 11, fc of 4.9, cc of 0, ph of 7.5 and alk of 64. I buy 2 cya, it comes in 1.75 pound bottles.

I go home and use what I have left with Ben's kit and my new taylor k2006 kit. My reagents with Ben's kit are 2 years old.

Both kits test chlorine at 6.5 fc and .5 cc. pool store 0, me 1
PH shows color of about 7.4, close enough. pool store 1, me 1
alkaline shows 80 on Ben's kit, 90 on taylor. pool store 0, me 1

But the cya test is not so clear.


I mix the reagent and let it sit while I do all the tests. Using Ben's kit, it looks like cya = 30. I can still see a little of the black dot, but I'd say 30 is close enough.

The taylor kit goes to 100, but it tops out (bottoms out?) at 30. When I fill it and look down, even waist high, I can see the black dot. Only a little cloudy. I can't tell if I have 30, 20, or 10.

Taylor tells me I have much less than 30, Ben's old kit says about 30.

So it seems to me I have more of a testing problem than a cya problem. But I did but in 7 or 8 pounds already this year. I did not drain, but we have had rain. So that may account for some loss of cya.


I am adding about 3/4 pound cya tonight, and 1.5 gal of bleach to shock. My water is clear, but there is algae trying to grow in the folds on the bottom.