Another case of the mysterious CYA-eating bacteria?!?

[styopr]

Man oh man, I wouldn't believe it, if I didn't see it. This is my second year of owning a 22-thousand-gallon pool and the CYA mysteriously "disappeared". About a month after opening, in June, the CYA level tested at 40ppm and the pool chlorine demand seemed normal. I have been using liquid chlorine with the BBB method. Usually takes a 1/4 gallon a day. The only time I use tabs is when I am out of town. Last week, after returning from vacation--when I accidentally left the chlorine tab floater adrift but closed for 10 days--I came home to a cloudy pool. I performed a SLAM which quickly cleared things up. Crystal clear. Except for this last week, my pool has been eating chlorine. Like lots of it. Gallons a day. Last night I shocked the pool again with 2 gallons of 10% liquid chlorine (thinking there may be still lingering bacteria eating my chlorine), and the FC rose to about 9ppm and stayed there. About 9 am the next morning tested at about 5ppm FC. Then zap! 11 am went to zero. Suspected I might need to raise my CYA level. Not having a CYA test on hand (just ordered one), I brought a sample to the pool store. I was thinking I might need to raise it from 40ppm to 50. But he got a zero reading! Here are the other specs:
PH: 7.6 (what I'm measuring too)
Alkalinity: 90 (confirmed by me)
Calcium: 175
Free Chlorine: 0 (same reading as me)
Tootal Chlorine: .5

To confirm the zilch CYA, I purchased test strips with CYA readings on them (not that accurate, I know but all I could find). Again- zero reading. Nada. I'll confirm again at another pool store, but I did buy some walmart stabilizer: granular CYA. I raised the FC Again tonight to 10 and it stayed there after an hour and have now added stabilizer socks to the skimmers!

Appears to be a confirmed case of disappearing stabilizer, or? Now, if I can only package and sell it! When I first bought the house and opened the pool last year the CYA was at a whopping 170 or more so I performed multiple partial drains and refills and threw in a package of bio-active CYA reducer. The CYA reducer didn't seem to do anything at the time but is it possible some of the bacteria remained dormant for a couple years until the right conditions (warm pool zero chlorine)? Hmmm.... seem unlikely it would survive the shocks, pool going up to about 15ppm fc on opening. But... it's gone...

 

[wireform]

It's definitely not ammonia otherwise it wouldn't hold FC. Could it be your just under the 30 and that could be difficult to decipher. I doubt the cya eliminator will ever do that kind of thing.

 

[styopr]

It's definitely not ammonia otherwise it wouldn't hold FC. Could it be your just under the 30 and that could be difficult to decipher. I doubt the cya eliminator will ever do that kind of thing.

Could be... pool guy performed Taylor black dot test and got a "zero" reading. He did a double-take and tested again because he thought something was wrong. The test strip I used showed the same color as tap water. I'll take a sample to a pool store with a digital readout (for what its worth) to compare/confirm with a third method/reading and get back.

 

[jake556]

Interesting, In AZ with the intense sun during the summer we lose CYA around 10-20 ppm per month. And the way I notice it is my daily FC increases similar to what you seen. It shocked me the first few times it did it.

 

[Donldson]

If I am reading this correctly, you are not using a good test kit? If that's the case you cannot be certain what you CYA level has been and can't really say if it disappeared overnight, over a couple months, or wasn't even there when you opened. Test strips are absolutely worthless and pool store testing is absolutely worthless. Don't waste your time taking it to a store with digital testing because that also is (say it with me) absolutely worthless. So there's no way to diagnose what may or may not have happened. I can say with all certainty that your theory about BioActive is not possible.

BTW, how is it you performed the SLAM Process without being able to accurately test your water?

 

[styopr]

If I am reading this correctly, you are not using a good test kit? If that's the case...

What makes you say that? I'm using a good test kit: Taylor K-1003 with a FAS test. As I stated, it lacks a CYA test. Theoretically (according to the literature) CYA is stable and once the level is established it doesn't need to be tested again or at least that frequently. The original CYA test both in May and June was performed by a Taylor test kit at the pool store (K-1721 I believe). Regardless of the test results, I KNOW that CYA was established at sufficient levels because of the water's ability to hold chlorine during the peak sunshine hours. As mentioned, the chlorine demand was about 1/4 gallon 12.5 percent solution per day. Now, when the sun hits it, the chlorine goes almost immediately to zero. So I have test results AND I have corroborating chlorine demand events. To your point, however, it could have diminished over the last month and a half. But, this would not correspond with the evidence that it suddenly -- in the last week -- started to demand much more chlorine.

 

[Newdude]

Theoretically (according to the literature) CYA is stable and once the level is established it doesn't not need to be tested again or at least that frequently

Correct. But you need a solid level to start with and the ability to verify yourself if anything gets wonky. A pool store dude performing an outside test indoors at the beginning of the season doesn't cut it.

The daily FC demand throughout the season is like a bell curve. You can be wrong to start the season or still just get by without enough CYA but once the season ramps up further than your protection, you're up a creek.

Spend the $30 and get your own kit. We can then start over with now results and keep you doing well after fixing the current issues.

Regardless of the test results, we KNOW that CYA was established at sufficient levels because of the water's ability to hold chlorine during the peak sunshine hours.

It held during the peak sunshine hours of that time in the season. It's now the peak sunshine hours of the peak season for loss. Maybe it was close for a while. Maybe it dropped just enough to matter. You just don't know when relying on other folks.

Help us help you.

 

[styopr]

Correct. But you need a solid level to start with and the ability to verify yourself if anything gets wonky. A pool store dude performing an outside test indoors at the beginning of the season doesn't cut it.

I appreciate your confidence in me! I'm beginning to think the margin of error with those tests can be wide, regardless of who performs them. I do agree as per the suggestion I have a pentair CYA test on order and I was able to find an HTC black dot test locally, which came with a real limited supply of reagent.

The easiest reading to identify is probably zero: no cloudiness. Possibly, it was low to begin with as theorized and went to zero through natural degradation.

Regardless, the results are in for today: after dissolving 2 lbs of CYA overnight in socks in the skimmer, got a reading of 15 from a different pool store (blinded, with no context), which would align with a zero reading to start with.

This evening, after dissolving another 2 lbs or so of CYA I got a reading of 30 doing my own "black dot" test. I dissolved another pound or so CYA after that for a total of about 5-6 pounds.

As you state, at least we know with certainty that it has 5-6 pounds of CYA so at a minimum should be around 30ppm if the pool gallons are near correct.


The pool is holding free chlorine like nobody's business. Almost a full day of sun in MN with some afternoon clouds. Pool is like clear glass. I haven't added anything, started at 4ppm FC, remains at about 4!

 

[Newdude]

OK GREAT !!!! Now comes the leap of faith part. Overnight Chlorine Loss Test with clear water. You had all kinds of time at or below minimum. If algae got a foothold, you're on your way to Swampville, you just can't see it yet because it's microscopic and grows exponentially. Those last few growth cycles are a doozy.

Prove you're clean. SLAM Process if not.

 

[styopr]

OK GREAT !!!! Now comes the leap of faith part. Overnight Chlorine Loss Test with clear water. You had all kinds of time at or below minimum. If algae got a foothold, you're on your way to Swampville, you just can't see it yet because it's microscopic and grows exponentially. Those last few growth cycles are a doozy.

Prove you're clean. SLAM Process if not.

Indeed, I have lost no measurable chlorine overnight. Exactly the same reading. 4ppm FC at 9pm. 4ppm at 9am FC. And it is actually holding steady in the sun! Think I am good until the next problem creeps up

 

[Newdude]

I have lost no measurable chlorine overnight. Exactly the same reading. 4ppm FC at 9pm. 4ppm at 9am FC.

Awesome !!! Thanks for clarifying that you've actually passed an OCLT, even if it was a roundabout way and not specifically done. However you worded it above left some question to me. Maybe it's just me. I'm a bit of a spaz.