Duelling TA and pH

[wayner]

I am having a **** of a time of a time getting both pH and TA in the right range. My pH has generally been too high (<8) and my TA too low (<100). But when I add MA to decrease the pH it tends to overshoot and the sample comes out way too yellowy. I then put in some Aqua Trol to increase the TA and the pH goes up too high again. I must have added over 1 kg of Aqua Trol to increase TA but it still measures about 60 with my K-2006 test kit.

Anyone have any advice?

 

[jblizzle]

Why do you want your TA so high? How are you determining how much acid to add?

 

[wayner]

My understanding is that TA for spas should be from 100-120. Determining how much acid to add is tricky since I don't know the exact pH. I have been adding about 4 fl Oz of MA. On second thought I guess I should use the base demand test - is that the way to do it.

FYI - I am using the K-2006 chlorine kit for my bromine spa but that doesn't matter for pH or TA as far as I have been told.

 

[jblizzle]

Oh, you did not mention this was for a spa ... although now I see the sub-forum.

I do not think the TA needs to be high for a spa ... the aeration will drive the pH up faster with the higher TA.
The demand test would be a good idea.

 

[chem geek]

Unless you are using a very acidic source of disinfection/oxidation such as MPS (or Trichlor, but that isn't normally used in spas) then you don't want your TA to be very high and even when using MPS you probably don't want it much above 80 ppm. Spas have a lot of water aeration, especially if you use the jets, and the water is hotter so there is a lot of carbon dioxide outgassing that tends to make the pH rise. Having the TA lower will lessen the amount of acid you need to add. The bottom line is that if your pH tends to rise in your spa, then lower the TA. If you have to lower it to 50 ppm then I suggest using 50 ppm Borates most easily added using boric acid.

 

[wayner]

Thanks - I use bromine tabs in the spa and a non-chlorine shock every few days. I am away fm home for a couple of days but when I return I will post the composition of the tablets.

So I won't worry about the low TA - good to know. We keep the water at 100F and do use the jets, including air.