Can't get my pH down after a fresh fill

[Mdragger88]

After adding baking soda to raise the TA and then dosing with 0.3 fl.oz MA followed later by 0.5 fl.oz of MA, my pH is now 7.7 and my TA is at 75! I really think I just blew up the pH on fill day between the main pump running on low all day to bring the cold water up to temperature and me running the jets for a long time while after I added the calcium to raise the CH.


I'm not sure what you mean by the two-bottle method or the chlorine neutralizing solution. My pH test is just a single vial with some phenol red. But I doubt it's high chlorine throwing it off. I was getting these readings before I added any chlorine.


Fill water TA is 70 with a pH of 7.6.

Great
Now just manage ph when it rises & the ta will fall further mitigating the frequency/intensity of ph rise.
No need for baking soda unless ta goes below 50. This will probably rarely happen if you aim for mid 7’s with your acid doses.
Also, if you need to use baking soda in the future go light handed with it. A little goes a long way in a small spa. You can always add more later. The same goes for all the chems until you are sure of their effects/ have your volume pretty dialed in.

 

[RDspaguy]

add calcium for my own nefarious purposes

I am just trying to simplify it for him. I am not opposed to calcium, but he can leave that on the back burner for now until he gets his ph under control. Priorities, ya know.

think what I need to do is add baking soda to raise my TA (since i'm at 50 now) in order to give me some more room to drop the pH further with more acid.

The very see-saw I sought to avoid with my advice. You are adding ph increaser then adding ph decreaser. Ph and alk are flip sides of the same coin. What you do to one, you do to the other. Ph is fast and only needs a little, and alk is slow and needs alot of chems, but they drag each other around. Leave it alone for a few days and see where it lands. Adjust ph from there. Get ph right then see where the rest is.

water TA is 70 with a pH of 7.6.

So what's the problem? That's a leave-it-alone situation. Occasional acid to counter aeration and chlorine and you're good. It shouldn't be a struggle, just a frequent chore. Any time you're adding counteractive chemicals in a rollercoaster of balance you're doing something wrong. Step back and let it settle.

 

[dougbr]

15 oz of boric acid should stabilize it around 7.6. Borate acts as a buffer against pH rise the same way that TA buffers against pH fall. Right now when you add acid, it reacts with the TA (carbonates) to produce salt and carbon dioxide. The carbon dioxide lowers the pH, but eventually it off-gasses from the water and the pH goes back up. Aerating speeds up the off-gassing.