can old pool plaster affect pH?

[gcthomas84]

Could old pool plaster be why my water is very acidic?

I bought a house with a gunite pool about 3 years ago. I never asked when the pool was built or if it was ever re-plastered. So let's assume the pool was built in 1980 and it was never re-plastered. I have to add soda ash about every month to keep the pH above 7.2. It was 6.8 about two years ago before I started adding soda ash. With enough soda ash i have gotten the pH to 7.8, but it always turns acidic. I feel like the amount of soda ash I am using to maintain this pool is ridiculous and I'm missing the bigger picture. When I talk to other pool owners in the area, they don't seem to have acidic water. If anything their water is too basic.

I hear that plaster can last 5 - 20 years. What happens when it goes bad?

 

[Patrick_B]

Well, it doesn't drive the pH down, that's for certain. Welcome to the forum.

What are you using for Chlorine, and what is your pool, and fill water TA (Total Alkalinity)? I imagine you have a healthy amount of TA in your fill water, so I will look for the answer to the initial question first.

 

[Richard320]

Welcome!

Are you, by chance, chlorinating with pucks and adding "shock" every week or whatever? Trichlor and dichlor are both very acidic. That's all I can think of. The normal course of things in California is very hard alkaline water that requires a bunch of acid. In five years, I've never added Borax, Soda Ash, or Baking Soda to my pool.

When plaster goes bad it starts flaking and chipping and cracking.

 

[gcthomas84]

Thanks for the replies.

I am chlorinating with pucks and adding shock about every 2-4 weeks during the summer.

The total alkalinity of pool water is at least 180 ppm. I'm using a strip tester so it could be more.
The TA of the fill water is also at least 180 ppm.

I don't have problems with plaster flakes or chips so maybe the plaster is more like 10-20 years old.

 

[duraleigh]

Almost certainly, your use of pucks is driving the pH down.

Switch to liquid chlorine and your pH issues should be over.

PS - you didn't ask, but your CYA is possibly far too high. If your CYA is as high as I think it might be, you need to address that issue

 

[Patrick_B]

That's what I was thinking about too, and figured it was pucks. If you really want to get ahold of things, you're going to need a new, and proper test kit. You simply can't run a pool well with the strips.

 

[gcthomas84]

Is there a difference between conditioner and stabilizer? CYA seems to be the ingredient for both.

My stabilizer level is at least 150 ppm, so indeed it could be way too high. Is chlorine less effective with too much stabilizer? That would suggest I am adding too much chlorine to battle the algae and driving my pH down.

 

[Patrick_B]

No difference, just the name, and either is correct.

It's really not that the FC is less effective, but it takes more of it to do the same Job. Higher Cya means more FC to stay clear and free of Algae issues. Where it becomes a real problem is when you get Algae with high Cya.