Borates and lowering TA

[Puffin]

Interesting question came up in another thread. Why is it recommended to adjust TA before adding borates?

In some ways it seems like there may be some advantages to doing it after. Since borates slow PH change and very low PH helps out gas faster, it seem like it would be easier to keep the ph in the 7.0 to 7.2 range.

 

[JasonLion]

You can lower the TA with or without borates, but most people find it easier to do without borates. Once you add borates it takes dramatically more acid to lower the PH and dramatically more aeration to raise the PH back up. The net effect is the same, but the process feels much slower and people get much more frustrated when trying it with borates in the water.

 

[BlueWave8]

This is something I was wondering as well. Why is it that the addition of borates makes pH so much more difficult to change without increasing TA proportionately?

 

[JasonLion]

TA is a measure of the waters resistance to lowering it's PH. Borates are better at providing resistance to raising PH then they are at preventing lowering. Nominally those two are symmetric, but in practice the TA test lowers PH from where it is to very low, and borates have much less effect when PH is very low, so the TA test doesn't fully reflect the effect borates are going to have in the PH range we are actually interested in.

 

[chem geek]

If you are interested in technical details, I created a new topic in The Deep End called pH Buffer Capacity.