ph low

[wilcfr]

I would like to add a question. We have a 38000 gal. gunnite pool. We chlorinate with 3 inch tabs and shock with calcium hypochlorite. For years we had a problem with high alkalinity levels (200+), this year however that is not a problem (102), but we are having problems with our pH. Our Cl levels have stayed around 2ppm all summer, but we can not get or keep the pH above
7.0. Early in the season we were running around 7.1-7.2, but in June it dropped to around 6.8-6.9. We have put a lot of Borax (3.5 boxes) in the pool over the course of the season with little change. As I mentioned earlier our usual problem is Alk. not pH. Any suggestions would be welcome. We bought some soda the other day, but would rather not use it because of past issues with high alkalinity levels.

The pool is crysal clear with no algae problem, but the pH issue concerns us because of possible damage to our heat pump pool heater.

[Watermom]

Using trichlor pucks is probably your culprit as they are extremely acidic and will drive your ph down. When your ph appeared to drop to 6.8 earlier, it might actually have been much lower than that as most test kits don't show anything lower than that reading. You don't mention what your cya reading is, but if you have been using trichlor it may be really high. If that is the case, a chlorine reading of 2 is pretty risky. At any rate, continue adding Borax. Wait 4 or 5 hours between doses to let it mix well, then retest and redose until you get your ph between 7.4-7.6. Also, test for your cya level and repost with that info. If you find that your cya is really high, you might want to consider using something else other than the pucks to chlorinate with as they will continue to add cya. Hope this helps.

[wilcfr]

Watermom thanks for the suggestions, we use a pH meter to check the pool, it was a cheap investment to get a much more accurate reading.

[wilcfr]

Aylad with that in mind maybe we will give the pool a little dose of soda. I have forgotten when you want to up the pH but not the Alk do you broadcast or put it in the deep end?

[waterbear]

Sal soda will raise both pH and TA. It does not matter if you broadast it or put it in one place. You are thinking about the 'slug method; of lowering TA, which has been proven NOT to work. All slugging acid does is ruin the pool because of the pockets of very low pH created.
Baking soda will raise TA and cause a slight rise in pH compared to sal soda
Borax will raise ph with minimal impact on TA.

As far as your pH meter, are you calibrating it on a regular basis and storing it with the electodes wet? pH meters are only accurate if they are regularly calibrated against standard solutions and if the electrode is properly cared for. The ONLY kind of pH meter I would trust is one that uses a 3 point calibration (calibrated against 3 different pH standard solutions.)

[aylad]

Just to add a word to Watermom's advice, I would also bring the alk up to the 120 range. When using trichlor, the higher alk will help keep the pH from swinging so far and so fast. The fact that you had high alk before is probably why you didn't have as much problem controlling your pH as you do now, with lower alk.