CYA/pH/TA in an Indoor Pool

[Argosy]

Since my pool is public, I have to test (FC & PH) every 2 hours. TC once a day and Total Alkalinity once a week (i do this twice). CYA is not applicable since it is unstabilized indoor pool. I do Calcium Hardness test and calculate Saturation Index just because I know what it is, but it is not required. Everything is written down, so at the end of the week anybody who knows pool chemistry (like my maintenance superviser or city health inspector) can read it like a map of what was going on in my pool.

If you do the same for 3-4 days, you will have a very good idea of your pool's pulse. I noticed that on the days when nobody used the pool the PH raises faster. On days when I have more then 10 users it seem to slowly crawl up.

 

[chem geek]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

CYA is not applicable since it is unstabilized indoor pool.
:
I noticed that on the days when nobody used the pool the PH raises faster. On days when I have more then 10 users it seem to slowly crawl up.

So I hope the FC level is kept rather low since there is no CYA in the pool to moderate its strength. According to these regulations for Ontario, you are allowed to go as low as 0.5 ppm. There is no ban restricting use of CYA in indoor pools and when CYA is used the FC cannot be lower than 1 ppm so you could use 4 ppm FC with 20 ppm CYA which would be equivalent to 0.2 ppm FC with no CYA but with greater capacity/reserve so that you don't run out locally if your pool's feeder system and circulation are not good enough to maintain 0.5 ppm FC with no CYA consistently.

Normally the pH rises faster with activity since the water movement drives out carbon dioxide faster. So that's strange.

 

[Argosy]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

So I hope the FC level is kept rather low since there is no CYA in the pool to moderate its strength. According to these regulations for Ontario, you are allowed to go as low as 0.5 ppm. There is no ban restricting use of CYA in indoor pools and when CYA is used the FC cannot be lower than 1 ppm so you could use 4 ppm FC with 20 ppm CYA which would be equivalent to 0.2 ppm FC with no CYA but with greater capacity/reserve so that you don't run out locally if your pool's feeder system and circulation are not good enough to maintain 0.5 ppm FC with no CYA consistently.

Normally the pH rises faster with activity since the water movement drives out carbon dioxide faster. So that's strange.

You are right. The min. FC for my pool is 0.5 ppm. I usually start the day with FC=2.5, TC=3.0. By 7pm FC goes down to 1.0 ppm if I get someone in the pool and some sunlight through the windows in the afternoon. If it is cloudy outside and no users, it will stay at 2.0 ppm by evening.

I do find it strange too in regards to PH rise When pool is not in use. But I also noticed that if PH rises at 7.6, then It will drift up very fast to 7.8 and above. If I lower it to 7.2, it tends to rise by 0.2 per day very slow. So I try to keep it in between 7.2-7.6 range all the time.

 

[pabeader]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

I'm told that pH rise can be attributed in part to an elevated TA level. What do you keep it at?

 

[pooldv]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

A few things cause PH to rise.
Aeration, waterfall, bubbler, rain, swimming
Saltwater chlorine generators
High TA, the number is variable depending on your pool

Generally, adding acid to lower your PH will also lower your TA over time and they will find equilibrium. Some pools reach it at 80, 70, 60 even 50. I would continue to add muriatic acid to lower your PH and let your TA lower on its own. Or you can actively lower your TA 10 ppm at a time until PH stays stable for a week or more. Pool School - Lower Total Alkalinity

 

[Argosy]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

I'm told that pH rise can be attributed in part to an elevated TA level. What do you keep it at?

TA is between 80-100. I try to keep it at 100, so my Saturation Index is around 0.0 when PH is at 7.4.

 

[Argosy]

Re: Need an Azimuth Check; CYA/Chlorine vs PoolMath

A few things cause PH to rise.
Aeration, waterfall, bubbler, rain, swimming
Saltwater chlorine generators
High TA, the number is variable depending on your pool

Generally, adding acid to lower your PH will also lower your TA over time and they will find equilibrium. Some pools reach it at 80, 70, 60 even 50. I would continue to add muriatic acid to lower your PH and let your TA lower on its own. Or you can actively lower your TA 10 ppm at a time until PH stays stable for a week or more. Pool School - Lower Total Alkalinity

Ok, then my PH rise is due to aeration problem that I had in the past month. The plumber replaced the leaky pump yesterday (usually it lasts 6-9 months) and now I don't have aeration problem, so by end of the week I should see how fast/slow the PH shifts with new pump and no air.

I actually end up raising my TA bi-weekly to 100 from 80. Because 80 is my by-law minimum and I don't want it to see below that mark one day.

 

[chem geek]

It is unfortunate that the Ontario regs don't allow lower than 80 ppm TA because it would make the pH rise slower if it were lower. This is because TA is a measure mostly of bicarbonate in the water and is related to the amount of over-carbonation of that water. Carbon dioxide outgassing causes the pH to rise. Oh well.

As far as your FC level, with no CYA in the water the active chlorine level is high so you are exposing your patrons to more chlorine than necessary. Their swimsuits, skin, and hair will get oxidized much faster compared to 4 ppm FC with 20 ppm CYA. At 2.5 ppm FC with no CYA, the active chlorine level is over 10 times higher. Also, with an indoor pool you may need some supplemental oxidation to control Combined Chlorine (CC). A UV system can work for this or with high bather-loads one could use ozone (with offgassing ozone removal) or some use of non-chlorine shock (though that interferes with chlorine tests unless you get a special reagent).

 

[Argosy]

It is unfortunate that the Ontario regs don't allow lower than 80 ppm TA because it would make the pH rise slower if it were lower. This is because TA is a measure mostly of bicarbonate in the water and is related to the amount of over-carbonation of that water. Carbon dioxide outgassing causes the pH to rise. Oh well.

As far as your FC level, with no CYA in the water the active chlorine level is high so you are exposing your patrons to more chlorine than necessary. Their swimsuits, skin, and hair will get oxidized much faster compared to 4 ppm FC with 20 ppm CYA. At 2.5 ppm FC with no CYA, the active chlorine level is over 10 times higher. Also, with an indoor pool you may need some supplemental oxidation to control Combined Chlorine (CC). A UV system can work for this or with high bather-loads one could use ozone (with offgassing ozone removal) or some use of non-chlorine shock (though that interferes with chlorine tests unless you get a special reagent).

Will mention UV system to the owner, but I doubt there will be budget for this.
So, if I start the day with FC=3.0, TC=3.5, and by the end of the day I have FC=1.0 is more then enough for my pool?

 

[chem geek]

The FC without any CYA is harsher. I'm not talking about how much FC gets used in a day. I'm talking about the instantaneous active chlorine level which is what people notice in terms of oxidation of their swimsuits, skin, and hair. You'll still use the same amount of FC per day with CYA in the water, but the active chlorine level will be lower and less harsh on patrons. It will also be slower to produce disinfection by-products. So you might start with 6 ppm FC with 20 ppm CYA and end up with 4 or you can start out with 4 and end up with 2.

If they don't get a UV system, then another approach is to coagulate the bather waste to the filter. Europe does this with their DIN 19643 swimming pool standard where they use only 0.3 to 0.6 ppm FC with no CYA (0.2 to 0.5 ppm if ozone is also used) and they use iron or alum salts for coagulation/flocculation. There are several reasons why this system wouldn't work in most U.S. commercial/public pools since it needs outstanding circulation to maintain such low chlorine levels, but you can use HaloSource SeaKlear PRS Stage 1 and 2 which will do an amazing job moving many organics to the filter to be backwashed. This should cut down the CC you are seeing and cut down on chloramine smell because organics precursors will be removed before they react too much with chlorine. This may also cut down on your chlorine demand.

 

[Argosy]

Ok, thanks. I will research it further.