constant ph battle

[jhm]

I've got a constant battle with rising ph, and always have. It bugs me, but maybe something I just have to live with. A little feedback here always goes a long way so I thought I'd give it a shot. My numbers:

FC: 3.5
PH: 7.8
CYA: 35
TA: 70 (might be slightly lower)
CH: 250

I use MA to lower ph, but have to do it consistently. I only use bleach as a sanitizer, which I've read is demanding on acid.

I tested my source water, which is over 8.0 but I can't tell how far over with my test kit (k-2006).

Is there anything I can do, or just keep doing what I'm doing?

Thanks!

[waterbear]

when you lower the pH how low do you put it? The lower the pH the faster it will rise from outgassing of CO2.
What is the TA of your fill water?
How are you testing the water?

[jhm]

when you lower the pH how low do you put it?

Good question. I suppose I go from 7.8 to 7.2 or 7.4, something around there. I try to keep it in the recommended range. You think that's causing it to rise quickly?


What is the TA of your fill water?

110


How are you testing the water?

k-2006, I mentioned that already, but maybe I'm missing your question?

Thanks!

[CarlD]

Have you been adding baking soda to increase your T/A level?

Normal T/A levels are from 80 to 120ppm and you are low at 70. Ordinary Arm&Hammer Baking Soda (or generic) is the same stuff they sell as "Total Alkalinity Raiser".

You are adding MA to lower pH--that's normal. But you are bringing down your T/A with it and the aeration of your water (do you have a waterfall or fountain?) is, via the out-gassing Waterbear mentioned, probably what's driving your pH back up.

So you add more MA...and it takes your T/A down some more.

I'm not sure how to stop the out-gassing other than turning off fountains, waterfalls, pointing the returns DOWN so they don't roil the surface--and maybe using a solar cover when you aren't swimming. But Waterbear may have better suggestions for reducing it.

Meantime I'd get the T/A back up. If you have a vinyl pool you may consider raising it higher. If you have a concrete/plaster pool, you may want to just take it to the upper range. Again, all you need to do this is baking soda.

Again, Waterbear may offer a reason not to do this, but that's usually how we get pH to stop oscillating, unless, of course, you have another cause of the rising pH.

[chem geek]

waterbear gave you good advice last year in this post (http://www.poolforum.com/pf2/showthread.php?p=56348&postcount=7). 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?

I disagree with Carl on this one in terms of the recommended TA level. If the source of pH rise is due to carbon dioxide outgassing, then raising the TA level is only going to make things worse to accelerate the rate of pH rise and especially the amount of acid that needs to be added.

Do you have sources of aeration such as waterfalls, spillovers, fountains or returns pointed upward? I agree with Carl that turning off such features (if possible) and pointing returns so that they do not cause waves or breaks in the water surface should help. Did you get your plaster resurfaced? If so, then the curing of such plaster will have the pH rise (and the CH as well) and there's nothing you can do about that but add acid, but this effect will slow down a lot after the first month and should become very slow after a year.

In spas when using the Dichlor-then-bleach method, people sometimes need to get the TA down to 50 or even 40 ppm before their pH becomes stable due to the great amount of aeration in spas. They usually use 50 ppm Borates as an additional pH buffer and if you need to keep your TA low, even below 70 ppm, then you could do the same. Also, for your plaster pool, once you settle on a TA and pH level for pH stability you can then adjust your Calcium Hardness (CH) if needed to get to saturation index that is closer to zero (The Pool Calculator (http://www.thepoolcalculator.com/) will calculate this for you).

Richard

[CarlD]

Richard's right that you need to also look to a concrete/plaster pool (especially a new surface) for the source of your rising pH. If it's due to to the calcium in your pool walls, I can only suggest Richard is right you'll just have to wait it out.

If, however, you have a vinyl pool, then we need to see if pH rising is due to out-gassing, rather than some other cause. If it's due to the aeration, then Richard and Evan probably have better advice for you than me.

It's very odd to have a vinyl pool, with fill water with T/A of 110, and no aeration, have its pH rise so consistently. Normally we see that with concrete/plaster pools or with salt-water chlorine generators.

Even with aeration SO much rising pH has me baffled.

But please let us know if your pool has:
1) Concrete/tile/plaster versus vinyl or fiberglass
2) Salt-water chlorine generation
3) Fountains, waterfalls, or other aerating devices.

My vinyl pool has none of those things and it doesn't seem to matter if my T/A is 80, or 180ppm--my pH only seems to change if there's a clear cause (like leaving the pool for 2 weeks with lots of Tri-Chlor floaters). Usually, pH is pretty stable.

[aylad]

Just out of curiousity, how much dilution does your pool get with tap water? With a fill water pH of over 8, if you were constantly adding water from a slide, fountain, or a hose to replenish splashout, it could very well be contributing to the rising pH.

It's just an idea....

Janet

[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 (http://www.poolforum.com/pf2/showthread.php?p=56348&postcount=7). 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 (http://www.thepoolcalculator.com/) 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.