connection between air in the return and CYA consumption

[Kilgore]

Split from http://www.troublefreepool.com/threads/80300-Keep-needing-to-add-CYA-why-would-this-be
Please start your own thread rather than hijack another member's thread Butterfly

The only thing that has changed this year is that I have added solar heating panels - the evacuated tube type. The guy who installed these for me has had some issues adjusting these properly and for some reason the solar panels seem to be allowing air to enter my system - it bubbles out of the jets. Could too much air (or Oxygen) cause issues with the CYA? Or is it getting burnt out by the solar tubes?

Hello everyone, my first post here, but I have read this forum out of interest from time to time.

I have no pool problems, except (if you can call it a problem) I also seem to consume CYA at a higher rate than expected. I use granular stabilizer. Water level is kept within an inch of the middle tile line, I don't have too much rain (yeah, right!), don't overfill, all that. I consider myself an experienced pool owner with almost 20 years of great water. My pool is 95% used by just my wife and myself, so not much splash out either.

I have always been very suspicious about why CYA gets consumed. I have read the articles here about ammonia conversion, but never saw any indications that ammonia was an issue, water is about as good as it gets. I can't even tolerate other people's' pools I am so spoiled. Yet I will typically use more than 30 lbs of CYA per year. The pool does not get officially closed here in Texas, I just keep the solar cover on in the winter (locked gate, no kids, and alarm), and cut the pump to 4 hrs per day, with freeze guard on. Yet CYA is typically near zero at the start of each season. I will use 4-5 lbs per month during swim season. When the pool is closed the solar cover stays on to control evaporation, so I don't bother anymore with adding unneeded stabilizer which just gets wasted away in the off months.

After reading the above, I began to wonder, is there a possible connection between air in the return and CYA consumption? I have an old-style Uniclor brine chlorine generator, which uses a venturi for sucking in the CL gas from the generator. This also sucks in quite a bit of normal air, due to the nature of how the venturi works. Lots of bubbles at the returns. Anyway, sorry for the long post, I was just kicking this idea around, and looking for feedback.

Below are my numbers from the last test a few days ago, using the K-2006 test kit. I do a thorough test every few weeks, but test for CL and pH daily. All other numbers stay very stable, except the always dropping stabilizer (pun intended!).

I think the chemistry of stabilizer, and its consumption, is more complex than we might realize. It seems to be a common complaint on this forum.

FC: 5
CC: no reading, less than 0.5
pH: 7.4
CYA: 50
TA:120
CA: 220

 

[JasonLion]

CYA does break down from chlorine, but the process is normally so slow that it can essentially be ignored. However, some situations, especially high water temperatures can accelerate this process enough that it is noticeable. On the other hand I have never seen anything indicating a connection with air in the plumbing.

 

[ping]

During the summer I also lose a good amount of CYA, usually have to add some every month. We tend to run the chlorine on the high side due to a lot of little kids in the pool and the temp we run at is in the high 80's. The other day I checked my cell for buildup and the water coming out of the cell when I took it off was extremely hot. Right now, our solar runs for only about an hour or so a day and then drains at the end of the day. I think I have found the reason why my pool goes through a lot of CYA in the summer, thanks Jason.

 

[Kilgore]

Hi Jason, thanks for the reply. Wow, my 1st post moved to the Deep End! I guess that's a good thing.

Anyway, what do you consider "high temperature"? My wife and I do like the pool in the 90 deg F range. That may sound very warm to some, but during a hot Texas summer it's all relative, and quite refreshing, especially at night.

Also, note that I still lose almost all the CYA during the offseason, when the pool is "closed" (as I explained above) with CYA at 60 or so. This is over 6 months, so it would work out to 13 lbs going somewhere when the pool is cool. That's about half the rate of loss during the swim season, and the pump runs about half as much, thus half the venturi bubbles per day. Coincidence? Maybe.

This is not a big issue for me, just something that has always made me curious. When I saw the post today about someone saying he started having high CYA consumption after he had new solar panels installed, and it was causing bubbles, and never an issue before, it raised my eyebrows a bit. Maybe he just has warmer water now, or the much higher concentrated heat in the solar panels is the culprit as the water passes through. Come to think of it, during the morning before my pump starts circulating, there is a very warm layer of water directly under the solar blanket during the hotter months. Maybe this has a cumulative effect each day.

Again, thanks for all the great contributions here. Even an old pool dog like me can learn new tricks.

Edit: I did not mean to "hijack" a thread, sorry! I just thought it logically followed the OP.

 

[JasonLion]

I think of 95+ degrees as high temperatures, 85 as normal. Of course it doesn't just turn on suddenly at 95, it ramps up as the temperature and FC/CYA ratio increases.

 

[chem geek]

To put things into perspective, our pool is kept at around 88ºF but the CYA loss is very low at perhaps 2-3 ppm per month. In a hot spa that operates at 104ºF is is usually kept above 90ºF we see CYA drop at around 5 ppm per month. The other two factors that increase the rate of chlorine oxidizing CYA is higher pH and higher hypochlorite ion concentration so a higher FC/CYA ratio. Even so, this wouldn't explain the more rapid sort of CYA level drop you are seeing. Perhaps you've got a magical catalyst or enzyme in your pool that is accelerating the breakdown -- if you could bottle it you could make millions.

As for letting a pool go over the winter, the bacterial conversion of CYA does not always end up with ammonia but can go to nitrogen gas in which case you won't notice anything unusual upon opening except for the lower CYA level. So at least for pools that are let go over the winter we have a reasonable explanation.

If the CYA is getting oxidized by chlorine, then you should see a significantly higher chlorine demand from that because it takes 2.5 ppm FC to oxidize 1 ppm CYA. So a 10 ppm CYA drop would consume 25 ppm FC so if you have 10 ppm CYA drop in a month then that would be nearly 1 ppm FC per day of extra chlorine demand.

I also responded to the evacuated tube solar panels thread.

 

[SunnyOptimism]

Kilgore,

Occam's Razor type question - do you have a small water leak somewhere? Do you notice your auto fill float valve running a lot?




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[Kilgore]

Hi Sunny:

I don't have an auto filler. But as far as I can tell, there are no leaks. I've done the bucket test on the steps when the solar cover is off for a few days, there are no wet spots in the lawn, and water usage amounts are in the normal range, based on reading the water meter when I top off.

To Chem Geek:

Maybe the way the Uniclor chlorine generator works uses up the CYA quicker than normal by some mechanism? I don't think many pools use this type of system anymore. It drops the pH, so about once or twice a week I put some of the caustic (NaOH) from the cell into the pool, by a valve and FEP tubing I have added by teeing into the venturi. This means the pH does change between the high and low range. About 7.2 when I add the caustic, and 7.9 after adding. Maybe I should do the caustic more frequently to not let the pH get that high, but that is a bit inconvenient. Anyway, I don't claim anything "magical", just pointing out my observations. I'm very happy with my water, so adding CYA once a month is no huge issue. I am just curious what exactly is going on.

Some more background: I have had the Uniclor for about 15 years (rebuilt it a few times), and my CYA usage has always been high, this isn't something that suddenly happened. The first few years before I installed it, trichlor pucks were used, so of course there was no CYA decrease then! The Uniclor runs year round, since I don't have to worry about it freezing. This means my FC doesn't really drop much in the offseason, but it might dip a little sometimes as I don't test nearly as often in the winter, about one a week for FC and pH in the off season.

Thanks for all the replies.

 

[pragmatic]

Excellent thread~Thank you!
I'm in SE Texas and also experienced CYA loss more >3PPM/month. Some general comments from others on this forum had me double checking my methods and numbers (even tossed some of my reagents). I now supplement my Clorox regime with pucks (in-line set very low) and test more often for CYA.