A few thoughts about CYA

[gordyjamz]

In the 4 years or so that I have read the threads here, I can't count how many times newbies and veterans alike get into trouble with CYA levels. A question that has always been in the back of my mind is, why do we even bother using stabilizer in the first place? The common knowledge is that it protects the FC from being eaten by sunlight, and that by using it will save us the problem of 0ppm FC levels. If one tests their pool on a daily basis, like most here do, I would think that one would notice a low FC level and immediately correct it by adding more Chlorine. This, to me would eliminate the need for stabilizer. The problems this product causes seem to outweigh it's benefits. Chem Geek has graced us with his knowledge of these things. CYA inhibits FC's job of oxidation. Why would we use a product that effectively would strangle chlorine, just so the chlorine would be there after a days worth of sunshine? It just doesn't make sense to me anymore.

My pool, for example, under trees, is only in direct sunlight maybe 2 hours out of the day. We also swim in it almost on a daily basis. So, I can't help but wonder if the FC I lose periodically is due to swimmer load, or sunlight. I can never know, because I have always had CYA in the pool. I may not even need CYA since I'm only getting a few hours of sun. Since I have to keep a higher FC because the stabilizer is in there, it could be costing me more $ in the long run. I could be keeping a 1-3 ppm FC with 0 CYA, as opposed to the 6ppm I shoot for now with my 40 CYA. That first 1-3 ppm that's being held in a headlock could be free and ready for the battle, should it arise.

So here's the deal. Next season we are having a new liner installed. Since a full drain/refill will be done in the spring, I think I'm gonna try no stabilizer. I realize it's ways off yet, but it's something that has always bugged me, and I want to try it. I will, of course, post here my thoughts and results.

Thanks for bearing with my sort of rant lol

Cheers,

Ken

[Watermom]

Hi, Ken. I think you'll have to do one of two things. Either add quite a large dose of chlorine to make you be able to make it through the day without losing all the cl to the sun. Or, add it several times each day which will probably be a big pain. Especially on days you aren't home throughout the day. If you do option #1 - large dose of cl, you may fade your liner or swimsuits. Just my thoughts. It is amazing how fast a pool with no cya loses all the chlorine. How well I remember that from my first summer I opened my pool years ago. Good to see you back around the forum.

[chem geek]

Ken,

The problem is not CYA, but too much CYA relative to the Free Chlorine (FC) level (or conversely, too little FC for the CYA level).

Without any CYA in the water, the FC level in most pools will drop by 50% every hour around noontime in direct sunlight. In your situation with only two hours of sun, the FC might drop by 75% (assuming the sun is on the pool near noon in the summer), but for most pools what you propose is impractical unless one has an automatic dosing and measurement system.

Also, without any CYA in the water, normal FC levels are too strong and would oxidize swimsuits, skin and hair too quickly and produce more of the most volatile and irritating disinfection by-products such as nitrogen trichloride (see this post) and increase metal corrosion rates as well. The problem is that it is very difficult to maintain only 0.1 ppm FC in the pool (with no CYA) which would be a more-than-adequate level to prevent algae growth and kill pathogens quickly (the min. FC level in most of Ben's chart is roughly equivalent to 0.06 ppm FC with no CYA).

The CYA acts as a chlorine buffer holding the chlorine in reserve as needed so its use is much more than just protecting chlorine from breakdown from the UV in sunlight. The fact that it moderates chlorine's strength (i.e. the active chlorine, hypochlorous acid, level) is a good thing. In fact, I recommend that it be used, in moderation, in indoor pools -- at a level of 4 ppm FC with 20 ppm CYA to give a little more oxidation power in indoor pools since there is no assistance from UV in that case.

Every year, my wife experiences the difference of having CYA in our outdoor pool vs. swimming over the winter in a community center indoor pool with no CYA (and around 1-2 ppm FC). Her swimsuits degrade over just one winter season (the elasticity gets shot) and her skin is flakier and hair frizzier while in our outdoor pool none of these problems occur. Our pool has typically had around 3 ppm FC with 30 ppm CYA (it has an opaque electric safety cover) so is roughly equivalent to 0.1 ppm FC with no CYA. It's no wonder that with the indoor pool having 10-20 times the active chlorine level that the degradation of swimsuits, skin and hair was so noticeable.

Richard

[waterbear]

CYA per say is not the problem, it's the misuse of CYA and the over use of stabilized chlorine products that cause problems. Proper use of CYA and stabilized chlorine is actually one of the best things that have happened to pool sanitation. Unfortunately, too many people use stabilized chlorine products improperly and run into problems.

[gordyjamz]

Thanks everyone for the replies. And, Richard, as always your in depth knowledge reigns supreme and is greatly appreciated. Ok, so your saying that it would be nearly impossible to hold a steady FC level with no CYA in the water, even with only a few hours of direct sunlight on the pool. What would you suggest as a rock bottom minimum level the CYA be at in my case? The sun hits between 1 and 3 pm during June and July. May, Aug, and Sept, it's more like 1 to 1.5 hrs of sun. Could I get away with the numbers you would suggest for an indoor pool? Some of my curiosity lies in a possible savings of $ when it comes to chlorine. And, also in the possibility of increasing the FC effectiveness. Then again, if it only would lead to $20 to $30 savings a year, and leave me with nothing but frustration it's not worth it. I guess the saying, "if ain't broke don't fix it" comes to mind here. I may still try no CYA at first to see how it goes for a week or so. Like I said, it's a ways off yet, but since I'll have the opportunity in spring, who knows?

Thanks again everyone,

Ken

[chem geek]

The indoor pool recommendation has a higher active chlorine level than you would need. Having even an hour or two of sunlight on the pool probably helps a lot in terms of UV breakdown of some organics (such as urea) and for airing out the pool for any volatile compounds. The minimum CYA would be 20 ppm though with your K-2006 test kit you can only easily measure down to 30 ppm so that would be the minimum.

So, 2 ppm FC with 20 ppm CYA or 3 ppm FC with 30 ppm CYA would be the minimum according to Ben's chart. However, note that your assumption that a lower FC results in lower absolute chlorine loss is wrong when a pool is exposed to a lot of sunlight. A pool with 8 ppm FC and 80 ppm CYA loses less chlorine than a pool with 3 ppm FC and 30 ppm CYA because CYA protects chlorine in a non-linear way shielding lower depths. However, in your situation with only 1-2 hours of sun, this effect may not be seen.

Also note that if you keep your water warm (88ºF), you may find a chlorine demand of 0.7 ppm FC per day even with no sunlight or bather load. So you want to make sure you have enough chlorine in the pool to not run out between your dosings. Having a higher FC and CYA gives you a larger chlorine buffer to protect you in case you miss a dose or when something unusual happens.

[waterbear]

Actually, you might end up spending MORE on chlorine with lower CYA levels than higher. Also, there is some evidence that at levels around 60-80 ppm there is some evidence of additional sun shielding effects from CYA that are possibly physical in nature, much like a sunscreen so even though higher FC levels are needed they stay stable for longer periods of time and overall chlorine loss is less.

[aylad]

It will be an interesting experiment, should you choose to do it!! I think you're going to find that you actually spend more on chlorine without the CYA than with it, because you're going to have to dose it so high on a daily basis to make sure that you have a residual. And don't discount shocking--should you have an algae outbreak (and that could easily happen if you get lazy for even one or two days about adding chlorine), then over half of your chlorine put in the pool to fight the algae will be gone to sunlight. I'm not sure that you could ever sustain a high enough level of chlorine to kill off algae without some CYA in the water.

I'm no chemist, but from a practical standpoint, I just don't think it would work...

Janet