CYA mystification...

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S

Steverino

LifeTime Supporter
Aug 18, 2009
97
Central PA
Happy Spring everyone!

So this is the beginning of Year Two with our vinyl in-ground. Last year we used the Nature 2 system that was included in our installation. This year I thought I would try BBB, so I'm sure I'll be on here a lot. :shock:

Did my first water test with our new Taylor K-2006 and am confused by the CYA result... I believe I followed the directions correctly, but I could easily see the dot even with the vial full (meaning a CYA of less than 30). Now here's the bizarre thing: as of 10-9-09, our pool store's test showed our CYA at 90. Other info - pool's still closed with winter cover on and no filtration.

From my understanding, CYA doesn't go away unless you change water, so what am I missing here?

Thanks,

Steve
 
You could easily lose that much over the winter. Rainwater is the primary culprit. Add to that the fact that pool stores are often inaccurate in their testing.
 
Thanks for the ideas, John & Scott... I wondered if my results could be some combination of what you each posted. Guess I won't worry too much about it until I get the filter started up (but that won't be for a while yet). Right now just trying to get my arms (& head) around BBB & what I need to do. :hammer:
 
The disappearance of CYA over winter has been a mystery for some time. I'm in eastern PA and mine goes to below measurable amounts from 60 at closing in October. In my case it can't be that it sinks to the bottom because I agitate the pool water before I run tests; even so, CYA will be way below 30 when I open.

In some pools, perhaps in some areas of the country, CYA does seem to go way over winter.
 
If a pool is "let go" over the winter with the chlorine level getting to zero, then bacteria can convert the CYA into ammonia thereby lowering the CYA level and creating a seemingly insatiable chlorine demand upon spring opening. This is described technically in this post and my personal experience with this phenomenon (by accident) is described in this post.

As was noted, winter rain dilution is another way for CYA to get lowered. Other causes for a drop are still a mystery, but we may figure it all out at some point.
 
chem geek said:
If a pool is "let go" over the winter with the chlorine level getting to zero, then bacteria can convert the CYA into ammonia thereby lowering the CYA level and creating a seemingly insatiable chlorine demand upon spring opening. .
Click to expand...

My CYA is usually almost 0 when I open as well. Down from ~60 ppm on close. However, i've never noticed a large increase in chlorine demand on opening nor a particularly large CC level either, as you might expect with a high level of ammonia (I've never tested for ammonia on opening the pool, but I plan to this year just to see what it might be).
 
My CYA went from 50 to 25 over the winter but I know without a doubt what caused mine to drop. It was rain. We've had a terribly lot if rain this year and I know I've drained an amount that would equal 3/4ths the pool volume over the course of the winter.
 
FPM: my test was done on non-circulating water (my pool is still "closed" for winter - i.e. winter cover is on, and pump & filter are drained). While my thermometer is not in the pool, the water is certainly cold :shock:, however the sample was room temp when tested.

I would not doubt some dilution due to rain and snow. Because the pool water was frozen for at least a couple of months, I don't know how much snow translated to actual water gain / exchange. That's one disadvantage to the winter cover - you can't see what's goin' on. I assume at least some snowmelt would have seeped through.

This discussion and related links that have been posted have made me think that maybe CYA buildup isn't as big a deal for folks in cold climates who close their pools for five or six months out of the year. Perhaps this is heresy - but I'm a pool newbie so I'll take cover behind that status :-D
 

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Say your pool is open for 6 months of the year and you add 2ppm of chlorine each day using trichlor. For each ppm of chlorine, trichlor also adds 0.6 ppm of CYA, over six months (182 days) that would be about 218 ppm of CYA. Even in just one season, starting at zero, you will start to have serious problems.
 
Hey, it was only an :idea: (perhaps a dim bulb) based on what I've begun to read and my meager one season. I started at zero and ended up at 90 (which I understand is higher than one would like). Probably would have been even higher as you suggest, Jason, were it not for our decent rainfall here in PA to dilute things.

I will be very interested to see if the readings change at all once I get the pump and filter running again.

Will also test for ammonia (I have an aquarium anyway) just to see if that's a factor.
 
Steverino said:
Will also test for ammonia (I have an aquarium anyway) just to see if that's a factor.
Click to expand...
Just FYI -- if you add chlorine to the pool and shortly afterwards you measure Free Chlorine (FC), then you don't have ammonia. Chlorine and ammonia combine very quickly (in seconds) to form monochloramine that measures as Combined Chlorine (CC) and not FC. Yes, you could use your ammonia test kit to test for ammonia if you want -- just note that it technically measures the sum of ammonia and monochloramine (if you haven't added chlorine to the pool yet, then if the test is showing ammonia then it's really ammonia). The ammonia test kit actually adds some Dichlor to the water sample to convert any ammonia to monochloramine and then a dye is used that measures monochloramine directly. So to recap,

FC = free chlorine only (hypochlorous acid, hypochlorite ion, chlorine bound to CYA)
CC = monochloramine plus other combined chlorine (e.g. chlorourea)
Ammonia test = ammonia + monochloramine

Richard
 
Thanks for the advice, Richard (and everyone!).

I do have one additional question that's related to the low CYA... As I look to start up the pool, I have lots of pucks left over, as the Nature 2 has a compartment to dissolve them over time. To reintroduce CYA, I assume I can run some pucks in the Nature 2 (sans cartridge of course), but I'm afraid the rate of CYA gain will be too slow (the pool is 28,000 gal, and they dissolve very slowly in the Nature 2).

The winterization kit I used has a floaty - I guess I could also throw some pucks in it for now.

Would I be better off just buying stabilizer instead?
 
I'm of a different opinion. Since you already have the pucks and you need CYA. I'd go ahead and drop them in the floater and use some if them up. It's not like you have to be in a big rush to get the CYA up. Just keep a check on your FC level while you do it. OF course that's just my opinion. :)
 
JasonLion said:
There are many ways to do it, and they all work. Personally, I would save the trichlor for use sometime when I was on vacation.
Click to expand...
Well, my 35-lb tub of 8-oz tabs would have started with 70 tabs, figure I need 3-4 (avg 3.5) for a week away, in practice not needed in the winter so figure two times a year, makes 7 tabs per year.... that is, one tub is worth about 10 years of vacations. :-D

I make it that the 35 lb of trichlor is cheaper than the equivalent 20 lb CYA + 30 gal 12.5% bleach, at least per Leslie's trichlor and CYA prices. I'll stick with trichlor for boosting my CYA each spring. While the water is still cold, low CYA is not an emergency, so I'm okay with it taking a few weeks.
--paulr
 
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