New Plaster/Pebble Pool - PH is stable only at low Alkalinity

[Connpatd]

Hi all.

My new plaster/pebble pool is around 4-5 months old and I was having issues with the PH rising to between 8.0 and 8.2 every day. I was trying to get the PH to stay at around 7.5 or 7.6 so each day I was having to add Muriatic acid to drop the PH. Well, Alk drops too when adding acid, so then I'd have to add Baking soda periodically to raise that back up into range (targeting 80 ppm). It's been a constant struggle. Add Acid to lower PH, then add Baking soda to raise Alk.

Well then I ran out of muriatic acid and my local stores were all out of stock, so I wasn't able to add acid for about 10 days. During those 10 days, my pool seemed to balance out at a PH of 7.7 and Alk of 50. Each day I tested PH and it was holding steady at 7.7. Then I added Baking Soda to raise Alk back up to 80 and the PH went back on the rise. I've since brought the Alk back down to 50 through normal PH adjustments using MA and PH is once again holding steady at 7.7.

Is it possible that my pool is just going to want a PH of 7.7 (which is still good) with an Alk of 50 (which seems really low)? Is there any harm to me keeping the Alk that low?

By the way, I am using Liquid Chlorine using the Pool Math Calculator.

My current pool numbers are:
16,000 Gallon Pebble Tec pool
FC: 6 ppm
CC: 0 ppm
PH: 7.7
TA: 50 ppm
CH: 450 PPM
CYA: 40 ppm

P.S. I have not been using my water features since I was afraid of PH rising even faster but I had a pool party last weekend and I did use the waterfalls. My PH and Alk remained in balance (7.7/50) even with my waterfalls running.

 

[ajw22]

Welcome to TFP.

Congratulations! You have found the pH/TA equilibrium point for your pool. TA of 50-60 with a pH anywhere in the 7's is just fine.

Stop adding baking soda and yo-yoing your pH and TA. Let your pH and TA find its natural equilibrium and don't force it to a number.

 

[Connpatd]

Thank you so much for your reply. I was worried the Alk was too low. I'll keep it right where it is, based on your response.

 

[setsailsoon]

I had the same problem 7 years ago and lowered TA to 50. As Allen points out above this works great and has no harmful impact. PH was much easier after this and ran 7.7 - 7.9. New pools can take up to a year or more before the pH stabilizes. In my case it was over a year. I eventually also went to a borate buffer. But I'd try TA 50 to see if this works first. For most it works fine.

Chris