pH too high (re-do without my email username)

[dfiletti]

Hey Folk, Dan here again. Nice to see the list up and running still, flourishing in fact.

So I opened the pool last weekend to a real mess.

So here's the story. The 25K gal. in ground, DE, SWG, irregular shaped pool was installed last spring with a Midnight Maui (dark gray in color) Hydrazzo. There were some streaks on the walls and a distinct line where the walls stopped and the floor began. I took this up with the builder and they had the plaster sub contractor come out and he agreed to do what I gather is called an acid start-up; whereby 20+ gallons of muriatic acid was added to dramatically lower the pH, and brushing occurred 2X per day for about a week. Once done he brought the pH back up. I tested a few days later and the pH was about 7.6.

The procedure did seems to homogenize the color, but the surface of my previously very smooth/ polished plaster was now more rough. It was late September, and I was about to close the pool, so I scheduled the builder to come out three weeks later (soonest I could get them out) to close the pool. In that three weeks my filter tank pressure rose to back-wash level (33psi), causing me to back-wash, 3 times. It was close to that pressure again when the closing crew came out. They close and cover the pool.

Fast forward to last week: I pull the cover off last week and the ENTIRE pool below the water-line is uniformly covered in about 1/2 inch of limescale. My dark gray pool was white!! I have been brushing and vacuuming/ brushing and vacuuming/ brushing and vacuuming all week and most of the limescale comes off. I am dealing with the builder on this, but I thought I'd throw it out there in case it's relevant. So about Wednesday, I run the gammut of test from the fine TF-100 here are the results:

Date: 5/20
Temp: 68F
FC: 1
CC: 1
TC: 2
T/A: 130
C/H: 370
CYA: 55
Salt: 3,200ppm
pH: Above 8

So, I up the SWG from 15% to 25% and I go buy 4 gallons of Muriatic acid, figuring I'd need it this summer. I have been incrementally adding 1/2 gallon and then waiting ~8 hours for it to circulate before testing and re-treating with another .5 gallon, (totaling 2.5 gallons so far) and the pH is STILL off the scale. Using the pool calculator in reverse it looks like my pH was at least 10!!

Questions:
1) Is there a way to measure how high my pH is?
2) Can I reduce my cycle times (been using a minimum of 8 hours before I tested and re-treated)? AKA: How soon after I add MA can I accurately test?
3) What could have cause the pH to rise so high?
3a) Could it have been the limescale?
4) Is there a better procedure than what I'm doing to get the pH down to ~7.6? I am concerned I'll overshoot.
5) My T/A and C/H are higher than my targets (100/ 250) would these be skewing my pH readings?

Any and all help you you folks would be willing to offer would be most appreciated.

Thanks,

Stay well.

Dan

 

[JasonLion]

There isn't any way to measure your PH accurately enough to be useful. There are some tests, which you presumably don't have, which could narrow it down a bit. If you have an acid demand test you can measure how much acid you need to use, without knowing what the PH really is.

You can retest the water, and add more acid, after 1 hour with the pump running.

As plaster cures it raises the PH, TA, and CH levels.

Scaling is caused by high PH, TA, and CH levels and actually lowers the PH a little.

You are doing the right thing, the only change is that you can be adding acid more frequently.

The TA will come down along with the PH when you add acid. Your CH level is only a little too high, that shouldn't be a problem once you get the PH under control.