liquid chlorine raising pH

I have read on other threads that NaCLO does not ultimately change the pH. With my 100k indoor 86 degree CL pool, whenever I add CL (12.5 %) I have to add about the same amount of HCL to maintain a pH between 7.2 and 7.6 I am wondering if this might be due to a high lye content in the liquid bleach.

Thanks for your thoughts,
Mike

The NET effect of adding sodium hypochlorite is close to pH neutral. It is alkaline when added BUT all forms of chlorine are acidic on sanitizing so that means that all of the unstabilized chlorine (sodium hypochlorite, calcium hypochlorite, and calcium hypochlorite) are essentially pH neutral and the main cause of pH rise is from outgassing of carbon dioxide. This can be lessened by lowering the TA, which should be between 80-100 ppm (or even slightly lower) when these are the primary chlorine sources in the pool. Second, the lower you put the pH the faster it will rise (because lower pH outgasses CO2 faster) so keeping the pH no lower than 7.6 will also slow pH rise in the pool.

When using acidic santizers (trichlor, dichlor, MPS, BCDMH, DMDMH) which are all net acidic then the TA should be higher, 100-120 ppm or even higher in the case of trichlor which is extremely acidic. This higher TA will have a faster pH rise to compensate for the constant 'acid' additions from the use of these products and keep the pH from 'crashing'.

Also, depending on how much sanitizer is added the pH can appear to rise after adding ANY chlorine or bromine source because of an interference between the halogen sanitizer and the phenol red pH test which causes a false high reading when sanitizer levels are too high. With some pH tests this can be as low as 3 ppm FC! With better tests (such as Taylor's) this is around 10 ppm sanitizer. The pH has not acutally risen as much as the test indicates and should be ignored until sanitizer levels drop to normal levels.

waterbear-
Thanks for your reply. My TA is kept between 70 and 100. I add about 25 gallons of 12.5 % NaClOH / month and about 20 gallons of HCL / month. 50 lbs of sodium bicarbonate is added about once every 5 weeks. That's all I ever add (except for calcium once in a blue moon) so it seems to me that the net change in pH for my pool when adding NaClO is significantly +

That's gotta be a big pool! Evan gave a really lucid explanation of when to keep TA on the low side and when on the high side--said it better than I could! The Taylor K-1000 OTO/pH test kit uses reagent r-0014 instead of the usual r-0004. r-0014 has a chlorine neutralizer in it so it can accurately read pH at much higher levels of chlorine.

If you need to raise pH AND TA, you can use Washing Soda instead of Baking Soda. Washing Soda is Sodium Carbonate, and is the same as pH Up! and other expensive pool chems, but only costs $.80/lb.

Costco used to sell 12lb bags of A&H baking soda for about $3.50. Yeah, less than 4 bucks for 12 lbs. Don't know what it is now....

Carl

I had a similar concern about chlorine and pH, and it came to light (thanks Carl) that aeration raises pH (outgasses CO2). Seems a public pool would see a lot of that.

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Originally Posted by Manslick

I had a similar concern about chlorine and pH, and it came to light (thanks Carl) that aeration raises pH (outgasses CO2). Seems a public pool would see a lot of that.

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Since our pool water is warm (86-88) CO2 is less soluble - and more is released.

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Originally Posted by CarlD

That's gotta be a big pool! Evan gave a really lucid explanation of when to keep TA on the low side and when on the high side--said it better than I could! The Taylor K-1000 OTO/pH test kit uses reagent r-0014 instead of the usual r-0004. r-0014 has a chlorine neutralizer in it so it can accurately read pH at much higher levels of chlorine.


Carl

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So does R-0004. The only difference is the comparator block used with them. The 2000 series comparator blocks for the R-0004 are a higher precision test better suited to commercial pools.

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Originally Posted by SalvationArmy

waterbear-
Thanks for your reply. My TA is kept between 70 and 100. I add about 25 gallons of 12.5 % NaClOH / month and about 20 gallons of HCL / month. 50 lbs of sodium bicarbonate is added about once every 5 weeks. That's all I ever add (except for calcium once in a blue moon) so it seems to me that the net change in pH for my pool when adding NaClO is significantly +

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So every 5 weeks you are raising the TA by about 36 ppm (from 70 to a bit over 100, I assume)...As a suggestion only raise the TA to 80 ppm. I think you will find that your acid demand does decrease and if you are adding less acid you will not be 'eating up' TA as quickly. The amount of bleach you are adding is really immaterial here. What you are seeing is the effects of TA on acid demand.

What is your target pH? If you maintain it higher (7.6 to 7.8) you will actually see better pH stability since the lower the put pH the faster pH rises.

pH is now 7.8 and I have not added any HCL since Sat. Ususally I have to add it almost daily. I am also maintaining CL at a lower level (1-3 ppm) FL code requires a min. 1 ppm CL in commercial pools....


Thanks waterbear!

I am in FL also and have cared for commercial pools.

It is the individual county Health Depts that set the standards. There really is not a statewide one but from what I have seen they are pretty uniform, at least on the east coast of the state.