Can't keep my PH down

[MaryS]

This is our 4th season with our gunite plaster pool. I have continuing problems fighting a rising PH. When we opened the pool last season, we had problems with calcium scale. Did alot of sanding, but lived with it. PH was fairly stable all season. After opening this year, we decided to acid wash and put all new water into the pool. The new fill water had a low PH. After only a few days, before the filter was even turned on again, the PH had risen off the charts. I have increased the alkalinity and lowered the Ph. The problem is that I have a continuing acid demand to keep the PH in the proper range. My numbers yesterday, before I added acid were:
FC 4.5
PH 8.0
ALK 100
Calcium 220
CYA 0

Did having the plaster acid washed cause this problem? How do I get the PH to stabilize. I don't want to have the scale problems again.

Thanks
Perplexed pool owner Mary

[aylad]

What is the pH of your fill water? I know that curing plaster will cause constant rising of pH, and I also know that many pools have a pH that they tend to stabilize at (mine will go to 7.8 and stay there if I don't do something to change it, and my efforts at changing it are pretty much just a waste of time and money!).

Since you have no CYA right now, you might want to consider chlorinating with trichlor for awhile since it tends to drive pH downward, and see if that helps?

Janet

[chem geek]

The sanding and especially the acid wash would produce a lot of plaster dust and would dissolve the plaster into the water as calcium carbonate which would raise the pH quite a bit as well as increase the Calcium Hardness (CH) and Total Alkalinity (TA) somewhat.

I agree with Janet that you just need to add some acid and using Trichlor would be an easy way to do this since you need to increase your CYA level anyway. Initially, you'll need a lot of tablets since they are slow to dissolve and the chlorine should get broken down by sunlight quickly due to no/low CYA, but soon that will change and a smaller number of tablets should suffice.

Richard