constant ph battle

[jhm]

Got distracted with some other things, and I didn't see some of the advice until this morning. Thanks for all the help!

To start, I'll make sure you know about my pool. It's a 25k gallon plaster pool with a spa. The spa spills over into the pool, so there is constant aeration that I can't really turn off. I also have a water feature that I run sometimes (my wife likes it), so that adds even more aeration. The pool is almost 10 years old, so it isn't a new surface issue. I stick to the BBB method, and do not have a SWG.

waterbear gave you good advice last year in this post. Did you follow that advice keeping the TA low (say, at 70 ppm) and having a higher pH target not below 7.6 and seeing if the pH rise to 7.8 is slow enough to be tolerable? Did you ever add the 50 ppm Borates?

Thanks for reminding me, it was actually two years ago. I did the Borates thing, that was a ton of Mule Team I added. To be honest, I wasn't crazy about the taste of the water after, but that's a separate issue. I haven't been religious about testing for borates since, so I'm not sure what the level is now. I honestly can't remember how much it helped stabilize my ph, but it did help. By now, without monitoring it, my ph is raging once again.

I'm thinking it is a combination of the constant outgassing and my source water. But now I'm confused whether to raise the TA or not.

Jim

[chem geek]

If your pH tends to rise, do not raise your TA -- that is clear.

[CarlD]

He'll need to keep adding acid and the waterfall will keep aerating and raising pH. Therefore the T/A will keep dropping.

But what effect will a low T/A have on the calcium in the plaster walls? That's STILL a separate question from the rising pH issue and has not been addressed.

If the plaster is at risk from low T/A, it's far less expensive to regularly add M/A and Baking Soda than to re-surface a pool prematurely. We cannot have a one-size-fits-all until you can show low T/A is not a problem for plaster surfaces.

[chem geek]

You don't have a low TA by itself. When you lower the TA, you raise the CH to compensate (or target a higher pH or both). You make the saturation index near zero (you can use The Pool Calculator to calculate the index). The saturation index calculates the saturation point for calcium carbonate and that is what protects plaster surfaces. TA alone is irrelevant. It is the combination of pH, TA and CH (plus some other less important factors) that determine whether there will be scaling vs. dissolving of plaster vs. a perfect balance.

Forget "low TA" or "low CH" causes dissolving of plaster just as "high TA" or "high CH" causes scaling. It is the combination as determined by the saturation index that determines the tendency (it does not determine the rate).

[jhm]

Forget "low TA" or "low CH" causes dissolving of plaster just as "high TA" or "high CH" causes scaling. It is the combination as determined by the saturation index that determines the tendency (it does not determine the rate).

Looking at the Pool Calculator was enlightening. So it seems if I keep my numbers just where they are, I'm in reasonable shape, but need to keep a close eye on pH. If I raise my TA, I'm actually in better shape according to the index.

I'm not sure where my borates are right now, but I did put a bunch in two years ago. Even if it is at 50ppm, though, it doesn't seem to affect the index. Maybe it helps stablize the pH a bit.

It sounds like the source of my problems is all the aeration going on in my pool (which is also one of the nice things about it). So I'll just need to be religious with the MA, and keep an eye on TA over time.

Does it sound like I'm making sense?

Thanks for everyone's help!

[jhm]

If I raise my TA, I'm actually in better shape according to the index.

After playing with the calculator a little more, I'm thinking maybe it would be better to raise my CH to about 300 (250 now). Then I can leave the TA where it is (but not let it fall lower) to help from raising pH.

Any thoughts?

[chem geek]

Yes, it would be better to raise the CH rather than the TA when your pool has a tendency for the pH to rise. Keeping the TA lower should help slow that down while raising the CH will protect your plaster surfaces by having the saturation index closer to zero.