where is my CYA disappearing to?

[dalejanus]

I have 28ft AG vinyl pool, 10,000 to 12,000 gallons.

When we open the pool every year, we have no CYA, and plenty of leaves in it. We clear out the leaves, add lots of bleach and add 2 bags of cya. Same thing this year.


But even after 2 bags (I think it's pounds) of cya, I did not get any readings. so we bought 2 more pounds and then the cya went up to 30 or so.

We got a little busy this week and FC went to .5. So I added 3 quarts bleach to take it up to 4ppm. But when I tested next day, I had no cya! Where did it go?

Naturally, with no cya, the sun is eating all my bleach. I added 3 gallons tonight and will test again in the morning.

But I wonder what is happening to my cya? I thought everyone said you cannot get rid of cya, you must drain and refill. I can't seem to keep it!

[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