Acid demand seems high

[mrafal]

First some background. Purchased this home early last summer with 12 year old pool. Had four months of use history before it was drained in preparation for replastering. Prior to replastering, the pH remained very stable, requiring the addition of MA only a couple of times over the four months.

Fast forward and I am now three months after replaster and I am adding in excess of one gallon of MA each week to keep the pH in check. I've added Borax to spread the dosing period from daily to a couple of times a week, but of course the total MA is the same.

For reference, my levels are:

FC 2.5 - 3
pH I dose down to about 7.3 when it reaches 7.8
TA 70
CH 300
CYA somewhere around 30-50 (that test is a bit subjective!)
Borate 50

I was expecting an increase in acid demand for the first year, but this amount has surprised me. Is this normal for a 15k gallon pool. Can I anticipate the acid demand beginning to taper some number of months after new plaster.

As a side note, it appears that the pool calculator (which I love) does not account for Borates in the calculation of MA dosing to adjust pH.

 

[JasonLion]

New plaster tends to raise the PH very rapidly for about three weeks and then more slowly for about a year. The initial rapid period can be somewhat slower and last significantly longer if the water temperature is fairly cold.

 

[Guest]

pH I dose down to about 7.3 when it reaches 7.8

The more you lower the pH the faster it will rise. Instead of dropping it down that low try just lowering it to 7.6 and when it hits 7.8 bring it back down. You ARE going to have a very big acid demand after a new plaster job for about the first year. This is completely normal. Just bit the bullet and keep a lot of acid on hand. You will see the demand start to slow after about 6-8 months.

 

[mrafal]

pH I dose down to about 7.3 when it reaches 7.8

The more you lower the pH the faster it will rise. Instead of dropping it down that low try just lowering it to 7.6 and when it hits 7.8 bring it back down. You ARE going to have a very big acid demand after a new plaster job for about the first year. This is completely normal. Just bit the bullet and keep a lot of acid on hand. You will see the demand start to slow after about 6-8 months.

Thanks for the suggestion. I'll give that a try.