pH & TA from a Newbie perspective
Let me start by saying I am by no means an expert in this area. What knowledge I do have is a result of reading many excellent posts by Waretbear, Chem Geek and others, while making just about every mistake a newbie could possibly make.
Once I got my Taylor 2106 kit I was bound and determined to get my water numbers perfect but really didn’t understand the pH – TA relationship so I found myself chasing my tail adding acid then baking soda over and over again. Looks like many others have found themselves in the same boat, so I’m posting this from a Newbie perspective.
1) Set your CH properly - I have mine @ 150
2) Set your TA to 80 (this is only a starting point) and stop believing that somehow it will magically stay there and don’t freak when it drops. I was testing almost daily and automatically added baking soda every time I got a reading below 80. Now I check it weekly and only add baking soda when it drops to 50. (add enough to return to 80)
3) Adjust pH to 7.6 and monitor pH every time you use the tub BUT only verify that it is between 7.5 and 8.0. Do not keep making adjustments if it’s within this range. I actually use a small OTO type test kit for this, not the Taylor, it gives a fast "Go / No Go" pH and BR reading. If the reading looks "No Go", I confirm with the Taylor and use the acid drop count to make adjustments.
Obviously aeration causes pH to rise and we all use the jets and air injectors in our hot tubs, so pH rise is an anticipated fact of life. Let it rise until it reaches 8.0 then adjust with acid. The addition of acid will lower the pH but the next time we turn on the jets, more bicarbonate will be outgassed thus lowering TA, but again don’t worry until it reaches 50. You’ll find that the pH rise will always be present but should slow down. Currently I find myself adding about ¾ oz. Muriatic acid weekly and about 3-4 ounces of baking soda every couple of weeks in a 350 gal tub.
I'm not sure what would happen if you don't add baking soda when the TA reaches 50 but like I said it takes a couple of weeks so it's no big deal.
BTW: This last water change I added 50ppm Borates (Borax + Muriatic Acid mixed in a bucket) The pH rise is still there but it gives you some peace of mind knowing that there is additional buffering so you don't panic when the TA hits 50 or lower.