Need help with PH and TA (long post, sorry!)

First off: 16 x 40 IG vinyl, about 6 weeks old.

I seem to have a problem with PH wanting to sit around 8 or above. My TA is 90. When we first installed the pool, I tested TA and everything else, TA was 80, and PB suggested increasing TA to around 130. He pointed to the information in the Pentair test kit that indicated if you use Cal Hypo, your TA should be 80 to 100ppm, and if you use Trichlor, your TA should be 120 - 140. At the time that was what I was using, so he added baking soda to shoot for around 120 - 130 TA. He said to get TA where I wanted it, and then see what happened with PH and adjust that if needed.

So, after adding the baking soda, TA went up to 130. In the last month since then, TA has been steadily dropping, and my PH wants to climb to somewhere between 8.0 and 8.4. I add muriatic acid, PH goes down to around 7.2, and within a couple of days, it's back up to around 8.0.

A couple of weeks ago, I took out the trichor sticks and switched to using bleach for regular sanitizing, and still using Cal-Hypo to shock. I've shocked a couple of times, trying to get rid of a little mustard algae, and to bring FL levels up during the huge amounts of rain we've had in the last couple of weeks. The information in the test kit says if I am using liquid chlorine, my TA should be around 80 - 100.

Should I try increasing my TA back up to 120 or so to prevent my PH from bouncing so much? If it stops bouncing, but wants to remain at 8.0 or above, should I keep adding muriatic acid? And then should I expect the PH to come down, but then remain more stable due to the higher TA? Am I overthinking this whole thing? I have been checking FC, TC, and PH levels every day. I am adding muriatic acid at least once every 2-3 days.

By the way, today's numbers:

FC 12 (added extra because we got 6 inches of rain from T.S. Alberto)
TC 12
PH 8.0
TA 90
CYA 40

are you testing the pH with the chlorine that high? If you are you are probably getting bogus pH readings. The Phenol red indicator for pH will give false high readings when the chlorine levels are above about 10 ppm (some cheapie kits it might be even lower. Pentair is one of them!) Don't test your pH until the chlorine is near normal levels and see if that helps. There have been many posts on the forum discussing this so I will not go through the chemisty of what is happening again.

Quote:

---

Originally Posted by waterbear

are you testing the pH with the chlorine that high? If you are you are probably getting bogus pH readings. The Phenol red indicator for pH will give false high readings when the chlorine levels are above about 10 ppm (some cheapie kits it might be even lower. Pentair is one of them!) Don't test your pH until the chlorine is near normal levels and see if that helps. There have been many posts on the forum discussing this so I will not go through the chemisty of what is happening again.

---

OK, good to know. But actually, when my FC levels have been between 5 and 10 (which is what I think it should be with a CYA of 40), PH is still bouncing some.

I think I will wait until my FC level is back below 10 before I make a decision. If my PH is still going high, with FC below 10, should I then try to raise my TA a little to see if I can stabilize my PH?

I would try and adjust the pH first and see how it holds. If it is bouncing then you might want to raise the TA a bit. Vinyl pools seem to do better with a TA of 100-120 as long as your calcium isn't too high. If your water is very hard you might get some cloudiness or scaling if the TA goes too high and the pH rises. I personally would check it when the FC is on the lower side of the range....maybe 5-6 ppm. Some of the phenol red just doesn't do well with higher levels. Depends on which test kit you have. Pentair is one of the ones more prone to the interferance from what I have seen from my own experience with their phenol red.

I just thought of something... the Pentair kit I am using tells me to add chlorine neutralizer (one or two drops) before I drop in 5 drops of the red stuff. Would the test still be skewed due to high chlorine?

I am also using a Walmart test kit, that test FC and PH. This one doesn't use the chlorine neutralizer. I bought this one because I was testing my FC and PH so much and didn't want to use up the DPD tablets in the Pentair kit.

I do notice I get a slightly different reading when I test the PH with both kits at the same time. I guess it is due to the chlorine.

The walmart reagent is corrected for chlorine interferance better than the Pentair. It already contains some chlorine neutralizer. Adding the neutralizer to the Pentair reagent will help but do not add more than 2 drops since the neutralizer itself can cause the pH of the sample to go up.