Sudden CYA Loss

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C

Cinic

0
Silver Supporter
Jul 24, 2015
194
Tempe, AZ
I'm stumped here and looking for input.

June 4 Test Results:
FC 3.0 (yes - low for my CYA - but never got below that and that was the only time I have been below min)
CC 0
pH 7.6
TA 90
CH 275
CYA 50

June 18 Test Results:
FC 6.5
CC 0.5 (just barely pink)
pH 7.6
TA 100
CH 300
CYA 20 (This one has me stumped)

I'd been having some unusually high FC demand on the order of 8 ppm per day. No significant overnight loss so I don't believe it was an algae issue. Did a CYA test (twice) just now and ended up with 20 and less than 20.

Initially, I thought I must have a leak and I've lost a bunch of water and it had been replaced with fill water thru the auto filler.

So I ran some tests on my fill water:
CH 125 or 150
TA 180

I've had no unusual acid demand or pH rise. In fact, the cup of MA I added this morning was the first I've added in over a week. If over half my water had been replaced (enough to lower my CYA from 50 to 20) my TA would be higher and my CH would have been significantly reduced? I guess that is a statement looking for agreement.

We got this pool about a year ago and it came with a CYA in the 70-80 range. I'd lowered it with back washing and splash out to the 50 and was going to ride that throughout the summer. But this high FC demand led me to discover that my CYA is disappearing.

What does anyone/everyone think? I'm going to start a bucket test tonight just to see if I find any leaking. Should start adding CYA back in and see if it stays?
 
Bucket test underway.

The chlorine never got below 3 or 3.5. Is that enough to have a bacteria infestation that would consume the CYA?

I've read a bit here about bacteria and CYA. Sounds like if that were the case I'd have a huge FC demand from ammonia which I have not had.

I'm adding back in enough stabilizer to go up to 50.

This is really confusing. I guess I'd rather be confused than have a huge leak though.
 
Well after 1 day of bucket test I show no significant difference. I really don't think I have a leak. It would have shown up in the TA & CH numbers.

The majority of the stabilizer has dissolved as of this morning and yesterday it seemed to hold the FC better. But it's tough to say where I'm really at until I know my CYA level. I'll give that a few more days to fully dissolve and register.

One thing to note is that there has been quite a bit of bird 'activity' around the pool lately. I've noticed droppings in the water. I wonder if some bacteria was introduced there.

My wife was also surprised at a water bill she opened yesterday. However, the meter was read on June 1. It was high - but really just trending up for the summer. And I had 50 CYA on June 4. We'll see what the July bill says.
 
Bacteria consuming CYA does not always convert to ammonia and stay there, sometimes there is enough bacteria present for it to continue through the nitrification process and ends up as nitrites or ultimately nitrates.

You can test CYA 24 hours after it is fully dissolved.
 
pooldv said:
Bacteria consuming CYA does not always convert to ammonia and stay there, sometimes there is enough bacteria present for it to continue through the nitrification process and ends up as nitrites or ultimately nitrates.

You can test CYA 24 hours after it is fully dissolved.
Click to expand...

Thanks for the input. Good to know about the ammonia.

The CYA should be fully dissolved today so I'll test tomorrow evening.

I'm still somewhat baffled by this. I *thought* I was doing a good job keeping the FC where it needed to be. Guess I need to be even more diligent...and stay away from the minimum.
 
I am a fan of more FC, not less. Pools are not closed systems, we get lots of help from outside influences that we probably don't even know about, like ducks! We often have some animal scat on our pool coping and I'm guessing they don't always miss. :shock:

Oh, and +1 to confusion and adding CYA vs a huge leak! :thumleft:

Consider raising you CYA to 60 or even 80. You've been around long enough to understand FC/CYA so it won't hurt you. It will noticeably cut down on your daily chlorine loss. Don't tell anyone but I accidentally raised mine to 100 a couple of weeks ago and I like it! I keep turning down the SWG trying to get FC under 10 so I can test PH.
 
Yeah - I inherited this pool last July with a CYA around 80. It had slowly lowered to around 50 via backwash and splashout over the past year and I had anticipated running throughout the summer with that number. Then this happened.

I had no problems managing the pool with the 80 last summer. You hear so often about too much CYA that I was kinda paranoid. I felt like I was doing something wrong when adding the stabilizer. :)
 
I know right! It is all in knowing what you're adding to the pool and managing the numbers. CYA at 80 is fine as long as you aren't "throwing" in pucks and bags of shock and what not from the pool store. Now, that you're a pro you can start experimenting with things a bit.
 

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So here's a question - if I had (or have) bacteria consuming my CYA, how do I know that I have (or have not) killed them? Besides waiting for my new CYA to be consumed again? Are bacteria typically large enough in quantity that I'd see demand on an OCLT?

Should I do a just-in-case SLAM?
 
A two day bucket test yielded no difference so that backs my suspicions that there was no leak. Also passed OCLT last night.

FC held much better yesterday using only 2.5 or 3 ppm during our 119° full sun day. Better than the 7.5 or 8 of a few days earlier.

I went back and studied my numbers from the past couple weeks. Somewhere around June 4 or 5 my demand started getting a bit high. Then it looks like it got worse around the 13th. I must have been keeping the bacteria at bay, but not totally wiping them out. Or they were being reintroduced via some other means. Just something else I know I need to keep my eye on apparently.
 
It's the least we can do. The fact that I've never set foot in a pool store due to this community has saved me hundreds and hundreds of dollars. Sometimes it is difficult to associate the 'value' of a place like this - especially a place on the internet where we're so used to things being 'free'.
 
I must have been keeping the bacteria at bay, but not totally wiping them out.
Click to expand...
I'd say you are on the money, cinic. Probably algae instead of bacteria but you would see similar symptoms either way and the solution is simply more chlorine. Nice work.

Thank you for you generous donation. The money is spent exclusively on forum expenses
 
Well, it is free, you are just giving TFP some of the pool store's money. LOL!

I am the same as you, 100% TFP from the start. No bad habits to unlearn or horror stories.
 
CYA tested between 40 and 50 yesterday. I added the balance (maybe 12 oz) of the 4 lb jug I got and it dissolved overnight. This should put me solidly at 50. I'll run with that for a couple weeks and decide if I should add more. I've got a trip coming up where I'll need to use some pucks in a floater so I'll be adding some then.
 

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