water hurts eyes and eats swimsuits, NaClO raising pH

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S

salvationarmy

0
Jun 17, 2011
57
NW Florida
I have been told by a few people that uor water is more irritating to eyes than normal, and suits are wearing out too fast. Here are some facts: 100k gallon pool, plaster, indoor, heated to 86-88 deg year-round, remodeled about 1 year ago, liquid chlorine (no salt),high-rate sand filters without any DE added (yet). Water is always clear, pH 7.2-7.6, TA 80-100, Calcium 250, FC 2-5 ppm, old test kit with a Taylor K-2006 on the way. My old kit does not detect any combined chlorine, but I do not trust it. Swim team practicing about 14 hours per week sweating in the very warm water. About 25 water aerobics seniors 3 times a week, plus about 150 other kids/week.
About all I add to the pool is NaOCL, HCl, sodium bicorbonate, and calcium (and water). I never have to add anything to increase the pH. On the contrary, I have to add almost as much HCL as I do NaClO (12.5%). I have been told by several reputable people over at the Pool Forum (which I just joined) the the Net effect of NaOCL on pH should be zero, so I am wondering what is up. The pool was allowed to have very high chlorine before I came on, and Chlor-out was used.
I have searched the forums some and noticed that a low TDS = osmotic pressure on the eye. I guess that my TDS may be low since the water was new about 14 months ago.
Thanks!
Mike
 
I am not an expert of pool chemistry of indoor pools, but I do know that at the pool where I teach swim lessons that we have a chlorine pump, an acid pump and add bicarb manually and the pH is always on the rise. Most of the rise in pH comes from aeration. Swim team member create a lot of splashing as do the general swimmers. This will naturally cause the pH to rise and you will have to lower the pH with acid.

I would guess that the burning of the eyes is coming from the high pH or CC in the water.

What do you mean by swimsuits wearing out too fast? What is too fast? In chlorine pools, lycra swimsuits will only last a few months with average use. Polyester suits will last a very long time - I am on year 2 with my polyester suit. Swim team members will usually have several practice suits that they rotate through to extend the life of them.
 
FC at 5 without CYA is very high and will tend to cause the problems you describe. With out CYA, keeping FC high enough to sanitize effectively and yet low enough not to cause problems is often a problem, thus the common use of chlorine neutralizer.
 
As Jason points out, it's most likely the fact that the FC is high with NO CYA in the water. CYA significantly reduces the active chlorine (hypochlorous acid) level.

My wife has personally experienced this difference every year when she goes to a community center indoor pool over the 5-month winter season where her swimsuits last only one season (the elasticity gets shot), her skin is flakier and her hair frizzier. In our own outdoor pool during the 7-month summer season, her swimsuits last for many years with hardly any noticeable degradation, her skin doesn't dry out as much and her hair stays in better shape. The difference is that the indoor pool is using 1-2 ppm FC with no CYA while our outdoor pool has an FC that is around 10% of the CYA level (roughly 3-6 ppm FC with 40 ppm CYA) which is equivalent to a pool with 0.1 ppm FC and no CYA. The active chlorine level in the indoor pool is 10-20 times higher than in our outdoor pool and that means chlorine is oxidizing swimsuits, skin and hair 10-20 times faster.

So having 5 ppm FC with no CYA is up to 2.5-5 times worse than the more typical indoor pool in the U.S. In Europe with DIN 19643, the pools are operated at 0.3 to 0.6 ppm FC with no CYA.

Using a small amount of CYA (say, 20 ppm) in an indoor pool can significantly reduce the problems of chlorine being too strong including the production of disinfection by-products. However, supplemental oxidation will be needed to oxidize the bather waste faster and prevent build-up of organic precursors and intermediates though in practice one needs that anyway since there is no UV from sunlight in indoor pools.
 
Thanks again to all for your time and input. Our pool does not have any CYA, and no supplemental oxidation. The European standard is very interesting.
I am now shooting for FC 1-3 ppm and pH 7.6 - 7.8. I have recently added CL without having the pH rise- it has remained steady at 7.6. Normally I would push it back down to 7.4 with HCL. TA = 85
FL code requires that I maintain FC @ 1-5ppm. Otherewise, I would consider going with the European standard (after some more research).

I do not have an automated system, and CL does fluctuated significantly, so it would be risky to try to keep it at even 1-1.5 ( I might end up with 0). Any suggestions? I do have a Stenner pump.
 

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Bama Rambler said:
I don't know if Fla restricts CYA in a public indoor pool but if it doesn't then about 20 ppm would help.

Tell us more about your equipment including the injection pump?
Click to expand...
Our Stenner pump is a model 45M4. Flow rate range is approx. 1.7 to 35 gpd. I also have a 30 gallon tank for chemical feed. I have thought about filling it with diluted NaOCL (even at the slowest rate, too much would be added with a 12.5% solution) and letting it run continuously (I do not have a timer control).

I got a new test kit today- Taylor K-2006. Combined CL is a disappointing .5 ppm, Cl is 2.8, pH is 7.8.
 
Also, if you use a 25 ml sample size you may find that your CC is actually 0.2 ppm or 0.4 ppm and not 0.5 ppm. Nevertheless, indoor pools are a challenge without the sunlight. Some people use UV systems that seem to effectively keep CC in check while others use supplemental oxidation.
 
Thanks guys. I did test with a 25 ml sample- I just estimated that it took a bit less than three drops to become sompletely clear when looking vertically through the water column. I have not shocked the pool (intentionally), but I have had the CL as high as 7ppm, before I knew that was excessive. We had a swim meet last night (lots of bodies in the pool). I tested this morning and found the CC to now be a little over .6 ppm. pH is 7.8. I tested for Cyanuric acid and confirmed that there is none from previous operators.
Another challenge that our pool has is turnover rate = 3 volumes per day, instead of the state required 4. Inspectors are aware and okay with it....

Can you guys recommend a CC solution for a tight budget?
According to Chlorine/CYA Chart by Chemgeek, shock for a 0ppm CYA pool is only .64 ppm? So going higher than my current 2.0 to shock the pool will not help? Will adding some DE to my filters help?

Thanks again,
Mike
 
The exact MPS dosage required depends on bather load to some extent. I would start at 1 lb per 10,000 gallons once a week and see how that goes. For higher CC levels you can use up to twice that much at one time and heavy bather load may require more frequent application.

For the Taylor FAS-DPD chlorine test you can eliminate MPS interference with a special reagent, R-0867, contained in the K-2041 and K-2042 kits, which include instructions and a calibrated dropper.

I mostly work with residential pools, so I don't have specific brand recommendations for UV systems.
 
Thanks Jason. Is Wipe-Out a good MPS shock? They could not tell me the concentration/other ingredients, and I have not found these details on the Web.
Would you recommend adding DE powder?

Should I try to shock with CL? (though according to the chart, my 2ppm is well above shock level).
How much sunlight does a pool need to significantly sanitize with UV? I am thinking about trying to get some more sunlight on the pool (without being filtered by passing through glass or acrylic)
 
In a heavily used pool, things perhaps work out slightly different from a domestic pool. I think the basic issue is that it takes time for chlorine to deal with the amount of pollution being introduced to the pool, especially when the turnover time is a bit low by modern standards. So even at adequate chlorine levels, you end up with combined chlorine. At least that's my theory. I'm not a chemist; perhaps the chemists on this forum will have a different view.

Earlier this week, I had the first complaints of stinging eyes in my pool (not really mine but a school pool that I manage). The FC had fallen to the minimum end of the range and both CC and pH had jumped up. Possibly all the playgroup children peed in the water earlier in the day. :grrrr: :grrrr: I think it's the CC that stings the eyes, or maybe the combination of CC and high pH, but I don't think it's pH alone since we've had pH at the top of the range previously and no complaints.

This forum teaches that the process of using up chlorine is pH neutral overall. However, I often find that my pH starts to go up when CC starts to climb. Giving the pool a rest from swimmers brings both down. So I think the first half of the process raises pH and the second brings it back to where you start.

Higher pH is supposed to reduce the production of tri-chloramine and "pool smell". However, if my pH were 8.0, I'd close the pool - to me it's a sign that I'm losing the CC fight and the pool needs some time off. I haven't tried MPS yet - although it has been suggested that might help me.
 

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