TA level

[65corvette]

I just completed the process of adding borates to my pool. I tested after 48 hours and the level is right at 50ppm. The pH is about 7.3 or so (which is fine I believe) but my TA dropped to 40 - input? I know I need to add baking soda, but I was curious as to why it dropped.

Thank you for all the wonderful advice!

 

[chem geek]

Normally, adding 50 ppm Borates will have the TA test slightly higher by around 5 ppm. If it dropped, then it might be that the pH dropped as part of your combined addition of Borax and acid. However, that would only account for a relatively small drop in TA -- going from a pH of 7.8 to 7.4 would drop a TA of 60 to 56, for example, so with adding borates the net TA change would be close to zero.

What was your TA level before it dropped to 40 ppm?

 

[65corvette]

It was 100 as I believe the directions indicated that it should be before beginning to add the borates. I tested the TA twice to make sure it was done correctly and it came out to 40 each time. :?:

 

[chem geek]

That's really strange. Are you using a drop-based TA test such as in the Taylor K-2006 (or 2005) or the TF100 from tftestkits.com? Other than some weird test interference (perhaps with test strips?) the only other thing I can think of is if you added acid before the borates and had the pH low for a time with some natural aeration, but that's a pretty substantial drop in TA. This seems to be a big mystery.

 

[65corvette]

I am using the TF100 test kit. I adjusted the pH before I added the borates. I followed the directions exactly adding 1/2 the acid immediately followed by 1/2 the borax. I brushed then repeated the process with the other 1/2 of each and brushed again. Well, I'll add the baking soda and hopefully then all will be well. I've never added baking soda - does that only effect the TA level and nothing else?

Thank you! :-D

 

[chem geek]

The baking soda may make the pH rise a little, but mostly it increases the TA.