CYA Dropped on it's own?

[Queequeg]

Since my pool was built in April, my CYA consistently tested at about 70 for about the first 2 months. I've been using BBB since day one so that it won't go any higher. I went on vacation for a couple weeks last month, and used Trichlor pucks while I was gone to make it easier on my neighbor. I wanted to see how much the Trichlor pucks raised my CYA , so I waited three weeks before testing CYA again, and now I have a CYA reading of 45. (I did it twice to make sure). I'm using a TFP test kit.

I don't backwash (cartridge filter), I don't have a leak (bucket test) so what could be making my CYA drop?

I have a theory that in very sunny/hot/dry conditions (such as southern AZ where I live) CYA naturally "disappears". Is there anybody else who has experienced this?

Can the Chem Geeks back this up or give any insight into what is happening? I currently use bleach for my chlorine source, but if my CYA is going to disappear naturally, I'll just use trichlor pucks as they are much more convenient.

13000 gallon in-ground gunite
Cartridge filter
No SWG
PH 7.6
ALK 90
Calcium 270

 

[JasonLion]

Having CYA disappear during the pool season without water replacement or algae involved is extremely unusual. The CYA level will drift down very slowly because of splash out and some tiny amount of CYA might break down naturally, but neither of these effects would normally be anywhere near as rapid as what you describe.

You said that you checked for leaks. Did you perhaps get algae, or have a couple of days when FC went to zero, at any time recently?

 

[chem geek]

I'm starting a technical post in The Deep End here on this subject. The bottom line is that there may be a slow degradation of CYA in pools at higher temperatures (above 85F -- so 90F or higher in particular) and at higher chlorine levels such as during extensive periods of shocking. In normal circumstances, the degradation is slower and probably overwhelmed by dilution effects (splash-out, backwashing, etc.).

 

[Swimgirl]

I'm in Southern Arizona, like you. When I first opened my pool, I put in a pound of stabilizer, shocked with dichlor a couple of times, and used trichlor in a feeder. After I found this site, I was still keeping track of my CYA using "guess strips" for a few weeks before getting my TF-100. I was surprised, upon getting my kit, that with all the CYA I had used, the reading was slightly under 40. So I think I had been experiencing a little degradation myself.

As far as tri-chlor in a feeder - I think that's more convenient than adding CYA on it's own, since you're getting your chlorine, too; but with our long swim season, and using a cartridge filter, even if CYA degrades a little bit on it's own due to the warm water; I think you would be asking for trouble if you use it more than occasionally. Remember, with CYA, you can put it in, but it's a pain in the a-- to take it out!

 

[Queequeg]

Having CYA disappear during the pool season without water replacement or algae involved is extremely unusual. The CYA level will drift down very slowly because of splash out and some tiny amount of CYA might break down naturally, but neither of these effects would normally be anywhere near as rapid as what you describe.

You said that you checked for leaks. Did you perhaps get algae, or have a couple of days when FC went to zero, at any time recently?

I didn't get any algae that I know of. (CC's have been zero every time I've checked).

I kept the chlorine level pretty high while I was on vacation for 2 weeks. (Had my neighbor throw in a couple pucks every few days). The FC was probably up around 10 for 14 days or so.

 

[Queequeg]

I'm starting a technical post in The Deep End here on this subject. The bottom line is that there may be a slow degradation of CYA in pools at higher temperatures (above 85F -- so 90F or higher in particular) and at higher chlorine levels such as during extensive periods of shocking. In normal circumstances, the degradation is slower and probably overwhelmed by dilution effects (splash-out, backwashing, etc.).

Hadn't seen this post Chem Geek. The pool temp is about 89F-90F from July to September around here. Could the high chlorine level I kept while on vacation have something to do with it? (See previous post above)

 

[chem geek]

Yes, that's the theory -- that high chlorine levels relative to CYA (so shock-like levels) and higher temperatures may lead to faster degradation of Cyanuric Acid via oxidation from chlorine. I question the actual rates, however, so think that this effect isn't seen as much at "normal" FC levels closer to 10% of the CYA level. I suppose that time will tell as we collect more real data from real pools.

 

[Poolidiot]

Well include me in the mystery CYA loss. I went on vacation for 3 weeks, when I left my CYA was at 40, when I returned the CYA is 0

 

[Queequeg]

Yes, that's the theory -- that high chlorine levels relative to CYA (so shock-like levels) and higher temperatures may lead to faster degradation of Cyanuric Acid via oxidation from chlorine. I question the actual rates, however, so think that this effect isn't seen as much at "normal" FC levels closer to 10% of the CYA level. I suppose that time will tell as we collect more real data from real pools.

If that's the case, and the effects are as dramatic as what I've witnessed, there may be a method to lowering CYA without draining water...

 

[chem geek]

Many people shock their pools and do not find a large drop in CYA, so I wouldn't jump to this conclusion yet.

 

[singerteacher]

Could it have anything to do with:
- the pool not getting "mixed" by swimming? (Could the CYA float to the top with inactivity?)
- the pool getting very hot at times? (I notice that the top few inches of water in our pool get really hot with direct sunlight when nobody is swimming to mix the top/bottom water.)

I'm nowhere near an expert ... I just like mysteries and theories!

 

[Queequeg]

Could it have anything to do with:
- the pool not getting "mixed" by swimming? (Could the CYA float to the top with inactivity?)
- the pool getting very hot at times? (I notice that the top few inches of water in our pool get really hot with direct sunlight when nobody is swimming to mix the top/bottom water.)

I'm nowhere near an expert ... I just like mysteries and theories!

In my case, the pool was still being "mixed" by the pump and cleaner every day while it wasn't being used. I do definitely think that the heat has something to do with it, as several people I know around here have used pucks for years without draining, and their CYA is fine. I'm really starting to think the "don't use pucks because of CYA buildup" theory may not apply to AZ.

As a test, I'm thinking I'll switch to pucks for a while and record my results. Right now it's a little low for my tastes, so it'll be interesting to see what happens.

 

[Swimgirl]

I actually think that the CYA buildup because of pucks does apply here in Arizona, maybe just not as much. Also, the ones who have been using pucks and say their CYA is fine might have:
1. Pool stores that have been testing their water and say, like some of them do, that any CYA under 200 is good.
2. Testing their own water and say the CYA is good when they are not entirely sure what they are looking for.
3. Lose a lot of water due to backwashing a lot or cleaning their filter a lot.

But as far as using pucks because you want your CYA to be a little higher - that's what I do. But only occasionally. Kills 2 birds with one stone - raises CYA and raises chlorine. Just keep an eye on your CYA, and don't raise your CYA too much! :-D

 

[branchop]

Are you having to add water a lot because of evaporation?

 

[Queequeg]

Are you having to add water a lot because of evaporation?

You betcha. The pool loses at least 1.5"-2" a week this time of year. At one time I thought I may have a leak, but the "bucket test" has shown otherwise. (Slightly humorous story: The first time I did the "bucket test" I placed the bucket on the deck rather than on the top step. It got so hot out there, the water evaporated from the bucket about twice as fast as the pool.)

I was under the impression that evaporation doesn't lead to a decrease of CYA. Is that correct?

 

[Queequeg]

I actually think that the CYA buildup because of pucks does apply here in Arizona, maybe just not as much. Also, the ones who have been using pucks and say their CYA is fine might have:
1. Pool stores that have been testing their water and say, like some of them do, that any CYA under 200 is good.
2. Testing their own water and say the CYA is good when they are not entirely sure what they are looking for.
3. Lose a lot of water due to backwashing a lot or cleaning their filter a lot.

But as far as using pucks because you want your CYA to be a little higher - that's what I do. But only occasionally. Kills 2 birds with one stone - raises CYA and raises chlorine. Just keep an eye on your CYA, and don't raise your CYA too much! :-D

Not that this proves my theory by any means, but my folks have had a pool for about 20 years here in AZ, and have used nothing but pucks to chlorinate the entire time. To my knowledge, they have never had algae (in fact they don't even test their water anymore, they just check once or twice a week to make sure 3-4 pucks are in it all the time).

This, of course, is horrifying to us TFP'ers, so I took my trusty TFP-1000 last time we visited. Their CYA was ~70 (which isn't too awful high with the full sun). The last time their pool was drained was about 6 years ago when it was re plastered. Our chemistry shows that their CYA should be out of control by now (remember in AZ we never "close" the pool, so it gets a steady stream of pucks all year long).

This, along with my own dramatic CYA reduction, is what led me to my "conspiracy theory".

 

[branchop]

If you lose water to evaporation and have to replace it with water that has no CYA, your CYA is going to drop. CYA doesn't evaporate with the water. The water you add for the evaporation dilutes the water with CYA.

This is why when your CYA is high the only way to drop it is to partially drain your pool and refill. So in essence, the sun is "draining" your pool and you are refilling. :-D

 

[frustratedpoolmom]

Actually Evaporation doesn't affect CYA like that. It becomes more concentrated, as the water evaporates. So say you have a CYA of 40....and 3 or 4 inches evaporates the CYA might increase slightly, hypothetically lets say 45, then you add more fresh water, which dilutes it, and puts it back where it was before, at like 40...

Draining, Splash out, or leaks reduces CYA. But technically, not evaporation.

I hope I explained that so it makes sense....

 

[chem geek]

Not that this proves my theory by any means, but my folks have had a pool for about 20 years here in AZ, and have used nothing but pucks to chlorinate the entire time. To my knowledge, they have never had algae (in fact they don't even test their water anymore, they just check once or twice a week to make sure 3-4 pucks are in it all the time).

This, of course, is horrifying to us TFP'ers, so I took my trusty TFP-1000 last time we visited. Their CYA was ~70 (which isn't too awful high with the full sun). The last time their pool was drained was about 6 years ago when it was re plastered. Our chemistry shows that their CYA should be out of control by now (remember in AZ we never "close" the pool, so it gets a steady stream of pucks all year long).

This, along with my own dramatic CYA reduction, is what led me to my "conspiracy theory".

Any idea what the water temperature is? Also, any idea of the typical FC level in the pool and the pH? Do you know the size of the pool in gallons? Does the pool have a sand filter backwashed weekly or a DE filter cleaned regularly (both of which would dilute the pool water)? Maybe the slow oxidation of CYA by chlorine becomes more noticeable at higher temperatures, but something still seems different here. Perhaps really strong sunlight also leads to some breakdown over time. We'll have to keep track of more pools to see if we can figure this one out!

 

[Queequeg]

Actually Evaporation doesn't affect CYA like that. It becomes more concentrated, as the water evaporates. So say you have a CYA of 40....and 3 or 4 inches evaporates the CYA might increase slightly, hypothetically lets say 45, then you add more fresh water, which dilutes it, and puts it back where it was before, at like 40...

Draining, Splash out, or leaks reduces CYA. But technically, not evaporation.

I hope I explained that so it makes sense....

This is exactly the way I understood it, and I think you explained it very well.