Pool temperature and FC?

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Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
129
Homer, AK
Pool Size
10300
Chlorine
Liquid Chlorine
I have an indoor, commercial, aquatic physical therapy pool in Homer, AK. I keep it at 95-96 degrees when clients are present. I have a question about whether or not I should increase the FC level because of increased temperature. This is an un-stabilized chlorine pool without CYA. The Phin Company that makes the gizmo that floats in the pool and sends info to your phone says: "Temperature also has an effect on chlorine, as some bacteria and organisms grow better in warmer environments. When temperatures increase, it uses up free chlorine more quickly, potentially turning your pool into a swamp.
Rule of Thumb: For every 10-degree Fahrenheit (6 degree Celsius) rise in temperature above 80 degrees Fahrenheit (26 degrees Celsius), you should add as much as 50% more chlorine to your pool water to maintain appropriate levels of free chlorine." I am wondering if the folks at TFP agree with this statement? I currently keep the FC at 3, plus or minus, PH at 7.3-7.5. This always gives me an ORP of 750 or greater. People like the pool. No trouble with skin, chlorine smell or bleached suits, etc. I am hesitant to lower the FC because I sort of agree that bugs do better in warmer water. Any thoughts?
 
Pardon me for saying, but if you're using a Phin only, you have no idea what your FC really is. Which is bad enough in a CYA 0 pool, but in a commercial setting that's really not acceptable. You need a proper test kit and you need to test your water at least daily, probably more considering how lack of CYA plus your other sanitizers can tank FC, then adjust your chlorine injection appropriately. The Phin might (might!) be accurate enough to keep track of a declining FC trend during the span of a day, but it's not accurate enough to determine the actual level. ORP and the test-strip "technology" on which a Phin relies is not something I would personally rely on, for my own pool, let alone in pool used by paying customers.

You should order one of these two kits today. Get a Taylor SpeedStir to make testing really easy and fast (like, two minutes fast once you get good at it).

www.troublefreepool.com

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why not use test strips? Our recommended test kits will pay for themselves in no time!
www.troublefreepool.com www.troublefreepool.com

Then the notion about water temp is a non-issue. You monitor actual FC through proper testing, and you dose chlorine to maintain FC. The water temp would then be irrelevant. The only way you can know your water is safe is by testing and maintaining FC. "trouble with skin, chlorine smell or bleached suits" is not enough to go on.

Sorry, though I did start out by saying "Pardon me!" ;)
 
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I have a Taylor kit (with DPD-FAS) and also use a Lamotte Color Q. I test for FC several times a day and feel that I have a very accurate reading on FC and all other levels in this pool. I also use a Hanna ORP/PH combo unit that gives me very accurate information on the true PH. I do not like the Taylor setup for PH which relies on comparing color.
 
Ah, I mis-read. So you're good to go. Just do what you're doing. Without CYA I would hesitate to suggest upping the FC to accommodate Phin's thoughts on the matter. Unbuffered chlorine would get pretty harsh pretty fast.

At TFP, we rely on the FC/CYA chart for sanitation. It's not temperature compensated. So that would be our official opinion on the topic. Now for our CSI calculations, that is temperature compensated, but CSI has nothing to do with sanitation.

Why no CYA at all? Is that a health code thing or something like that?
 
I’ve read that CYA is controversial and some real experts, along with many states, think it should not be used if not necessary. In my case the only reason to use CYA would be to make the Chlorine last longer. But I don’t think my chlorine usage is all that high so I would rather not use it. Getting back to my question though. I was wondering if I could lower my FC, not raise it. My TDS is now above 1625 and I am planning to drain and refill the pool on April 2. Our tap water has very low TDS. Just wondering if I could get by with FC in the neighborhood of 1.5 - 2.0? I’ve found that increasing TDS lowers ORP (but not that much). Water is pretty cheap here anyway.
 
TFP doesn't deal much with TDS. That's a pool store gimmick that doesn't reveal much about pool water. We track the actual salt level along with FC, pH, CH, TA and CYA levels, and find that's all that is usually necessary to maintain safe, comfortable water. And what we teach here is backed by real science and "real experts" and ignores old school methods that still linger around the industry (unlike the decades-old practices many self-proclaimed "experts" and state legislators still mistakenly rely on). And as I mentioned, we adhere strictly to our FC/CYA table. So we're not going to advise you to adjust your FC otherwise. We also contend that some CYA in the water not only protects your chlorine, but also your swimmers (from harsh chlorine effects). TFP's primary focus is on outdoor residential pools. Or more accurately, my knowledge is primarily on outdoor residential pools! Let's see if some of our experts can better advise you.

@mknauss, @duraleigh, @chem geek, I'm gonna need some help with this special-circumstance pool...
 
Thanks. I sort of feel like if it ain’t broke, don’t break it. I agree that TDS isn’t really that relevant, but I want to change out the water for lots of reasons. I have it down now to where I’m only using 2 chemicals on a regular basis but over the last 10 months I have added a lot of stuff that I realize was not good (crazy?). Now that I know more about what I am doing, I want to start with a clean slate. I want TA at 80, CH at 200, and I’ll keep the FC at 2.0 to start with. If the reports from the monthly lab tests start to get out of wack, I’ll take appropriate steps. I have come to realize that “set and forget” is out of the question. Thanks again for your input.
 

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Yah, sorry Bw, I knew your pool was out of my realm, but Marty's answer was what I kinda figured... Best of luck to ya.
 
Bwdonohues58 said:
I have an indoor, commercial, aquatic physical therapy pool in Homer, AK. I keep it at 95-96 degrees when clients are present. I have a question about whether or not I should increase the FC level because of increased temperature. This is an un-stabilized chlorine pool without CYA. The Phin Company that makes the gizmo that floats in the pool and sends info to your phone says: "Temperature also has an effect on chlorine, as some bacteria and organisms grow better in warmer environments. When temperatures increase, it uses up free chlorine more quickly, potentially turning your pool into a swamp.
Rule of Thumb: For every 10-degree Fahrenheit (6 degree Celsius) rise in temperature above 80 degrees Fahrenheit (26 degrees Celsius), you should add as much as 50% more chlorine to your pool water to maintain appropriate levels of free chlorine." I am wondering if the folks at TFP agree with this statement? I currently keep the FC at 3, plus or minus, PH at 7.3-7.5. This always gives me an ORP of 750 or greater. People like the pool. No trouble with skin, chlorine smell or bleached suits, etc. I am hesitant to lower the FC because I sort of agree that bugs do better in warmer water. Any thoughts?
Click to expand...
Yes, bugs do thrive better in warmer water. Pseudomonas is the primary concern in warmer water and it can be resistant to chlorine, particularly if a biofilm forms. The temp you are running is warm enough for pseudomonas to thrive. CYA should not be used in an indoor public pool. While this may be an option for private pools it is important to maintain the fastest possible microbial inactivation and CYA dramatically slows that down. I have inspected many pools that run close to 10 ppm indoors with no CYA. Once you get to 10 ppm you will start to see complaints about swim suits bleaching out.
Aside from temperature, another big factor is bather load. I would recommend aiming for 3 to 5 ppm FC as long as you are finding it remains fairly stable in spite of the bathers.
 
I missed the part about your ORP being over 750. If that is consistent you should be safe to lower your FC below 3 ppm. Again, that would still depend on how stable it is in the presence of bathers. Is there a constant chlorine feed or do you manually dose?
 
I add liquid chlorine via a Stenner pump. It runs for 4 hours before I open it up for the day. I check the ORP at 8:30 every day and it is always over 750. I check it again when we close at 4:30 and it's always still above 750. I should add that I also use a Spectra light UV unit and a Clear Comfort AOP unit to assist with ORP. ORP is also greatly affected by the PH. I keep it at 7.35 - 7.5 using 8 ounces of MA weekly. Bather load is also a factor. We usually have 2 clients plus 2 PT's at any one time in the pool. Our 2nd PT went on vacation for 3 weeks so we now have only 2 people in the pool at any one time. I've found that under these conditions, it's very easy to keep the ORP above 750 with no CYA and FC around 2.0. This pool room has a UV blocking coating on the 3 small windows. Under these conditions, I use about 1 gallon of 10% Liquid Chlorine per week. The guys at the State lab who test my water always say that I'm good. But as you know, pools are always changing so I have to stay on top of things.
 
It sounds like you are managing it well. If you were manually chlorinating I might have recommended a higher FC level to give you some buffer room if you encounter a high bather load but since your disinfection is automated and ORP is on target your FC level is definitely adequate.
 
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