Fighting The Ta - Ph Battle

[dan517]

Hi,

Just got my Arctic Yukon installed 6 weeks ago. For the life of me, I'm having a hard time getting the TA and PH in the safe zone . The PH always seems high, and TA low. The dealer, who tests my water, told me to bring the PH down to a good level, then bring the TA up which will also raise the PH and all will be good. I've tried this rooutine twice in two weeks (I get the water tested there once a week), but the result is always the same. I'm running bromine tablets, and that test is good. The only other thing I've added was calcium to bring the hardness up. Unfortunately, the only test method I have is strips, and from what I've read here a Taylor K-2006 is the test kit to get. Any ideas??

Thanks,

Dan

[chem geek]

Dan,

If the pH in your spa tends to rise or stay towards the high side, then there is no need to have the TA be high. The higher TA just makes the rising pH problem worse. Aeration and high TA (and low pH) make carbon dioxide outgas from your spa faster and that causes the pH to rise (this chart shows the relative outgas rates as a function of pH and TA). You can have the TA be low without any problem -- just have at least 50 ppm assuming the CYA isn't too high (if the CYA is 100, then the TA minimum would be more like 70 ppm). If you have a plaster spa or have tile with grout exposed to the water, then you'd need a high Calcium Hardness (CH) level to compensate for the low TA, but most spas don't need the high CH (because most are fiberglass or other non-plaster materials).

In a non-plaster non-tile/grout spa, the only issue with the lower TA is that it takes less acid to have the pH get lowered so you just need to be aware of that.

Richard

[dan517]

Thank you Chem Geek...so what I take from that is that in the case of a fiberglass spa, getting my PH to a proper level is more important that getting my TA up to the desired level...right? If that's the case, then all I should have to do is bring down my PH to an acceptable level. Thanks again!

Dan

[chem geek]

Yes, you've got it. pH is far more important than TA for a fiberglass spa. The industry thinks you need a high TA for pH stability, but they forget that the main component of TA, bicarbonate, causes the pH to rise especially with aeration due to the outgassing of carbon dioxide. Essentially, pools and spas are intentionally over-carbonated to provide a pH buffer and, for plaster surfaces (along with added calcium for calcium hardness), to provide saturation of calcium carbonate. Just as a lovely tasty carbonated beverage will go flat faster if you stir it up or blow bubbles into it through a straw, aeration in a spa drives the over-carbonation out of the water -- and this process causes the pH to rise with no change in TA for technical reasons I won't get into here.

I wouldn't feel bad about not just adjusting pH. Your TA would still have likely been too high if you switched to using bleach instead of Dichlor, so you still would have had to lower the TA. The good news is that once you've adjusted the TA to the place where it's fairly balanced, then spa maintenance becomes very easy.

Richard

[Whoneedsavacation]

Thank you Chem Geek...so what I take from that is that in the case of a fiberglass spa, getting my PH to a proper level is more important that getting my TA up to the desired level...right? If that's the case, then all I should have to do is bring down my PH to an acceptable level. T

FWIW I had the same battle on my first fill with my new (thermoplastic) spa. On the second fill, I've been following chem geek's suggestion and have allowed the TA to hover below 80 while watching the pH to make sure it stays in range. So far it's been working like a charm and I've been throwing a lot less "stuff" into the water.