Could CYA Help?

[subslug]

I've mentioned in a couple of posts on here that we've installed some pretty high end (read $$) UV systems in our indoor pools. The folks who install these systems swear that they don't eat free chlorine but all of my pool sense, and other indoor facility operators, tell me otherwise.

Isn't UV from the sun what is responsible for the higher chlorine demand in outdoor pools?
These UV systems virtually eliminate Combined Chlorine levels but, obviously they aren't smart enough to know good chlorine from bad, if they remove one type surely they'll remove any type good or bad?

I can attest to our chlorine demand rising at all of our locations since installing these systems, despite what installer man wants me to believe. What I'm looking for is another opinion that, if I tried adding and maintaining a CYA level of about 20-30, even though these are indoor pools, would I expect to see the Chlorine demand drop and what are the possible evil side effects of this CYA?

Our pools are primarily chlorinated with ORP controlled commercial SWGs with the occasional (more often lately) boost with Cal Hypo as needed to maintain FC levels.

Thanks in advance

 

[JasonLion]

We recommend CYA levels around 20 for indoor pools. Adding a little CYA to the water prevents high FC levels from damaging hair and swim suits, and reduces the production of some of the more annoying forms of CC.

You do need to be aware that CYA will have a significant affect on your ORP reading, lowering it noticeably. You will need to "re-calibrate" your ORP set points any time the CYA level changes. You also need to be very careful not to allow the CYA level to get too high. Since CYA reduces the effect FC has on ORP readings, other factors which change ORP readings become more significant. As the CYA level rises, you eventually get to the point where FC tracking is lost. This typically happens around a CYA level of 60 or 70, which shouldn't be a problem. But in some situations, when there is more than the usual amount of "noise" in the ORP reading, it can impact things at lower CYA levels

Another thing to keep in mind is that the common CYA test only tests down to 20, and it is +-10 at the best of times, so maintaining a uniform CYA level can be a little tricky. And, pool regulations in some areas do not allow any CYA in indoor public pools.

 

[subslug]

Thanks Jason

At the most I'm going to try and maintain a 30 CYA level.
I had actually tried to follow some advice from chem geek one time and added CYA to another of my facilities to try his theory on lowering my CC levels...for whatever reason I could never reach the 30ppm level we were trying to achieve. I kept adding but nothing ever showed up on the test so I eventually got scared off from adding anymore in fear I was going too far.

On this facility I'm going to go by your calculator and add liquid cya and see what happens.

In your best guess would you think that the UV system is probably using up chlorine? This CYA should help with that I'm hoping.

 

[JasonLion]

Yes, the UV system is using up chlorine. The counterpoint is that the UV system is also breaking down organics that would use up chlorine if the UV didn't break them down. Sometimes, those two effects balance out. But usually UV ends up using up more chlorine than it saves.

 

[chem geek]

In your best guess would you think that the UV system is probably using up chlorine? This CYA should help with that I'm hoping.

In theory, the CYA could help protect the chlorine somewhat from the UV system. It won't be as much as protection against sunlight for the pool as a whole since that effect includes CYA itself protecting lower depths of water. Nevertheless, since most of the chlorine will be bound to CYA, I would expect some protection. I suppose we'll see -- keep us posted.

If you have a test kit that measures CYA to 20 ppm, I'd just go to 20 ppm only. Or if you do go to 30 ppm CYA, keep in mind that you need a higher FC level. I'd shoot for an FC that is around 10% of the CYA level. We don't have as much experience with CYA in indoor pools so I'd rather be a little conservative with the active chlorine level though your UV system should take care of most problems associated with indoor pools (buildup of CC in particular).

Richard

 

[subslug]

I started this out last night by adding 3 gallons of the liquid stabilizer to this pool as per the calculator. I'll be back at that location tomorrow and I'll see where I stand as far as CYA level goes.
I may go and see if I can find a more comprehensive CYA test kit as this isn't something we normally test for at all.

I'm willing to deal with the higher chlorine demand as a result of these UV systems. The lower to non-existent CC levels not to mention the added sanitation provided by them plus the better air quality in the pool room far outweighs any added chlorine costs. With these systems we virtually eliminated having to shock our pools so we're probably using less chlorine compared to the operators who are still shocking......granted it's gonna take a LOT of chlorine savings to counter the cost of these UV systems.

I expect these UV systems to gradually become a fact of life for commercial pool operators.
Especially if every time the news catches wind of a Crypto. related illness and causes their widespread panic like they did last season. We just decided to suck up the costs and protect our swimmers. If you're teaching little ones how to save their own lives in the water, you certainly don't want that very water to put their lives at risk.

I'll check back here when I get some results of all of this.

 

[chem geek]

You can get the CYA test which measures down to 20 ppm at tftestkits.net here (or the K-1720 from Taylor here).

I agree with you that UV systems make a lot of sense in commercial/public pools since chlorine is so ineffective against Crypto (and not very effective against Giardia when there's CYA present) and that they are also useful in indoor pools to help reduce combined chlorine (CC).

Just so you know, having the FC at around 10% of the CYA level has the pool with an equivalent FC of around 0.1 ppm with no CYA. With the ammonia and urea from sweat and urine from the bathers, there will be higher monochloramine and dichloramine but lower nitrogen trichloride, the latter being the most irritating of the three -- it's about a factor of 10-20 difference between 1-2 ppm FC with no CYA and 3 ppm FC with 30 ppm CYA. The UV will help reduce all of these chloramines, but it takes time (multiple turnovers). The low active chlorine level due to the CYA will also likely reduce outgassing of chlorine -- mostly an issue in warmer pools.

So let us know if you notice any differences, after adding the CYA, in FC consumption, smell, CC measurements or anything else.

Richard

 

[chem geek]

I thought I would answer your chlorine breakdown from UV question a little more specifically. The peak (and range) wavelengths with maximum UV breakdown for chlorine and chloramines is as follows:

Hypochlorous Acid -- 236 nm (<200-260 nm)
Hypochlorite Ion -- 210 nm & 292 nm (<200-220 & 260-330)
Monochloramine -- 245 nm (225-265)
Dichloramine -- 297 nm (range unknown)
Nitrogen Trichloride -- 260 & 340 nm (range unknown)

Medium-pressure UV lamps have a broad spectrum with multiple peaks. The problem is that the peaks near 297 nm for getting rid of dichloramine will also break down hypochlorite ion which has a rather broad absorption from around 260 nm through 330 nm. There are strong peaks of UV from the lamp at around 297 nm, 302 nm and 313 nm.

Low-pressure UV lamps have a narrow spectrum with sharp peaks at 185 nm and 254 nm. They don't break down chlorine as much, but they also mostly only handle monochloramine (and some nitrogen trichloride).

Richard