Does Algae "Eat" CYA

[sevver]

Before I took over the maintenance, my wife did things the pool store way. She used bags of powdered shock to chlorinate. Took the water in to test every few days. Added what they told her to. Everything would be fine for a while, then algae would bloom up, they would say double the bags of shock added, or even triple them. Do this for a few days, and the pool would clear up, and we would go back to a bag a day again. Eventually it would begin again. She swore that it was a conspiracy, and that the pool stores added something to the mix to cause the algae blooms, thus causing you to buy algaecide, clarifier etc.

Well when we moved, I was told that she was done with it, so I found poolforum.com and started using the bbb method. Ever since then I have always wondered, if the bags of shock contained stabilizer, and it would build to a point where it would no longer be sanitary and a bloom would develop, using more of the same would cure it, and we could return to the original dosage. My question is, did the stabilizer get consumed, or did it just appear that way?

 

[frustratedpoolmom]

Appeared that way.

The higher the CYA, the more chlorine or sanitizer is needed to do the same job.

Overtime, it sounds like your CYA got so high that normal levels of Chlorine were no longer effective, what used to be enough was not anymore; why you had to triple the dose, etc...

I learned more than I ever wanted to know about CYA last year....

Live and learn right!

 

[sevver]

I understand the relationship between the need for more sanitizer at higher stabilizer levels. What I am curious about is does the stabilizer get consumed by the algae, or a reaction with the algae?

I have seen that the only way to lower CYA is through water replacement, but then I opened my pool this year with no CYA, and plenty of algae. And the year before, when I actually closed my pool the right way, by using a cover and bringing the Cl to shock level first for a day or two before covering it, when I opened it then, I believe that there was stabilizer left. So what happens to it?

 

[Matt]

"Eat" isn't really the right word, but yes, they do lower CYA levels by using it to create things they need. It's not really eating though, since AFAIK it's not an energy source for them, even if they use it as a substrate in a number of metabolic processes.

 

[sevver]

Yes, I did not mean eat literally, but it does consume it. How does it do that? What exactly does it do to reduce it?

 

[chem geek]

Steve,

I talk about what goes on in this thread at The Pool Forum. It isn't the algae that uses up the CYA, but rather soil bacteria that is allowed to grow because of a lack of chlorine in the pool. The bacteria converts CYA to ammonia (and other items as described in my post). I also talked about it (without showing the net chemical reaction) in this post on this forum.

Richard

 

[sevver]

Excellent. Thank you for the info. Just what I wanted. And what I expected, although with a different cause.

 

[Matt]

No organism can live without nitrogen, carbon, hydrogen, and oxygen in fairly substantial quantities. Other elements are needed to varying degrees. Nitrogen can be obtained from the air or from the CYA, depending on where the bacteria are and what substrates they need to produce what they are trying to produce.

 

[Guest]

The breakdown of CYA by denitrifying bacteria has been well documented in studies done on the breakdown of atrazine (a herbicide) in soil. One of the early metabolites of atrazine by pseudomonas is CYA which is then further metabolized to ammonia by other denitrifying species.