water hurts eyes and eats swimsuits, NaClO raising pH

[JasonLion]

Cal-hypo is fine as long as your CH level doesn't get too high. Using cal-hypo instead of liquid chlorine will not normally affect the CC level, but PoolDoc may well have some special technique that works. Higher PH is good up to a point. I like to keep it lower than 8.0 but that isn't a big deal as long as your TA and CH levels are not too high. High PH, TA, and CH levels can cause calcium scaling, so you do need to keep an eye on that.

Any amount of sunlight helps, of course how much sunlight you can get is going to be limited by your building design.

Shocking with chlorine can help a lot, but you need to balance that against getting the FC level back down before people swim again. Some people shock every night when the pool closes and then lower the FC level first thing in the morning with chlorine neutralizer. That certainly helps keep the CC level down, but it uses a lot of chemicals.

 

[salvationarmy]

loop_pea, thanks for your thoughts. FL Commercial Pool Code requires pH to be 7.8 or below, so I added acid to bring it into compliance. For anyone that may be interested, I have a similar post at another pool forum here:
http://www.poolforum.com/pf2/showth...on-Army-Pool-eye-irritation&p=76233#post76233

Thanks Jason for all of your input.

Mike

 

[loop_pea]

salvationarmy, thanks for pointing out that other post, very interesting.

The instructions on the other forum mostly seem to be about how to use cal hypo without blowing yourself up. I'm not sure why that works better than sodium hypochlorite though. The only thing I can think of is that dosing it into the skimmers allows small particles of calcium to sit on the filter, where they make the filter work more effectively. Letting the pH float up will enhance this effect since the calcium becomes less soluble. Perhaps DE would achieve the same effect? Plus bumping up the chlorine at the end of the day, so it works while there's no new pollution coming into the pool.

Note to self: I must remind playgroup not to let their darlings pee in the pool.

 

[chem geek]

Shocking a pool with chlorine at higher pH reduces the amount of nitrogen trichloride that is produced, but increases the amount of trihalomethanes such as chloroform. The bottom line, though, is that with a high bather load you need some form of supplemental oxidation. With outdoor pools, the UV from sunlight that breaks down chlorine produces hydroxyl radicals that are powerful oxidizers and may be what tends to keep CC in check by oxidizing organics (such as urea) and also breaking down some CC directly. With an indoor pool and especially with higher bather load you almost always need supplemental oxidation. Some pools use UV systems, some use ozone, others use non-chlorine shock (MPS). I think you are going to be chasing your tail if you try to solve the CC problem using chlorine alone, at least long-term. Having a chlorine level high enough to try and oxidize bather waste fast enough is going to also be high enough to cause faster degradation of swimsuits, oxidation of skin and hair, etc.

 

[salvationarmy]

Thanks again, chem geek. I am still trying to absorb and sort out the various and sometime conflicting advice that I am receiving here and at the other forum. Thursday I raised the CL to 4.5 and accidentally lowered the pH to 7.2. I did this by adding NaOCL and HCL. The CL held for 24 hours, and the pH gradually rose. CC dropped from .8 to .4ppm overnight. CC is back up to .6 now, with CL = .5 and pH 7.5. I just added some CL to bring it up a bit.

 

[chem geek]

What you are seeing is consistent with what I've been saying. A higher FC will tend to reduce the CC level, but the CC that is produced can be more irritating and the higher FC (with no CYA) will oxidize skin, swimsuits and hair faster and if very high can also be irritating on its own. Ben at The PoolForum isn't saying much different except that he didn't like using non-chlorine shock (MPS), but unless you get a UV system (or ozone) I don't see what other option you have for supplemental oxidation. His other suggestions on bathers getting cleaner before entering the pool are of course good, but you may not have much control over that.

 

[salvationarmy]

I would love to get a UV sytem, but the cost is prohibitive. Would a solar tube shining on our collection tank be much of a help? (Basically a skylight directed through a mirrored tube).

Thanks,
Mike

 

[chem geek]

It might help, but probably not that much because the amount of sunlight won't be very much relative to the surface area of the pool. Nevertheless, because you aren't using CYA, the chlorine will breakdown in sunlight faster and that breakdown is what creates hydroxyl radicals that can oxidize bather waste faster. You'll know the approach is working if you find that your chlorine demand increases during the day, even when there is no bather load. What is the surface area of water you would be exposing to sunlight as a proportion of the surface area of the pool?

As for the non-chlorine shock (MPS), you can always do a bucket or small tank test to see is any chemical will help with regard to CC. Just scale down quantities for the test.

 

[salvationarmy]

Chem geek-
Thanks again for your time and reply. My tank surface area is only about 1/450th of my pool area.
I like your idea of a bucket test with MPS. Do you (or anyone else) have any UV recommendations or advice? 240 GPM, 100k gallons.
Thanks,
Mike

 

[chem geek]

I don't know UV equipment, but someone else might have a recommendation.

 

[salvationarmy]

Thanks