Is there a certain window of time

[Rangeball]

Since the measured TA is dependant on the pH at which it is measured you might see this effect. If you measure the ALK at a pH of, say 7.8, and follow the procedure and then retest once the pH is back at 7.8 you will find that the measured TA is now lower. IF the TA is very high you need to keep the pH low as you aerate and keep adding acid to keep it low and also monitor the TA. You will see it start to decrease. When it has lowered then stop adding acid and aerate until the pH is where you want it, say 7.4. Your TA might read slightly lower at this point or not. The lower you can safely get the pH to and keep it there while you aerate the faster you will lower the TA in the water since you will maximize the amount of the buffer that is in the form of carbonic acid.

Hope this doesn't confuse you too much!

I believe I understood everything, and I believe I am following the procedure as outlined, what I don't understand is why I'm NOT seeing a signficant PH/ALK drop when I add the required amount of acid and aerate. Any ideas?

The only variable seems to be aerating WHILE trying to get the PH to drop, but I've eliminated this, so we'll see.

[Rangeball]

Tested PH at noon-

7.3, down from the 7.6 I got this morning. I plan to get more acid, and lower it until I have a 7.0 reading. At that time I'll retest ALK and start aerating again.

[Rangeball]

After monkeying with this all weekend, I have come to the following conclusion-

Aerating WHILE adding acid to lower PH is counter-productive.

I added more acid to get to 7 (actually just a hair below), waited until I got there then fired up the sump pump aerater. The next morning the PH was still 7, so I did a bunch of cannon balls and general splashing about, then left the aerater running while we were out of town. When we got back, PH was back up to 2, so I stopped all aeration and added acid to knock it back down. Started aeration and did a bunch more manual aeration, then checked PH again before bed, it was up to 7.3. Stopped aeration, added acid and went to bed.

Continued this process through Sunday. Got the alk down to 150, this morning PH was down to 7 again so I turned on the aerater again.

In retrospect, when I was adding acid with the air leak in my return flow, it apparantly was enough to prevent the PH from dropping low enough to get carbon dioxide production, so as the PH remained stable then rose, the alk went right along with it.

Now all I need is another gallon of acid and a few more days I have my fingers crossed I've finally figured this out.

Tredge, what did you come up with?

[Rangeball]

Ben's sticky says you need to get PH low to induce carbon dioxide production.

Once carbon dioxide is present, I assume it's no longer measurable as part of the ALK test, and this is why we get the drop, right?

And if it's not gassed off, when PH increases due to aeration, carbon dioxide reverts back to CA, which is measurable, right?

Anyone know at what PH level carbon dioxide re-converts to CA? Waterbear?

[Tredge]

I'm letting my TA sit high. I'm pretty happy with how the pool is balancing right now and the water looks better than ever.

If I do Aerate more out I'll probably build myself a fountain from PVC parts. Sounds like you need a Lot of aeration to make a difference in a larger pool.

Great news on your progress!

[Rangeball]

Thanks!

I think my rapidly escalating PH was related to the air bubbles in my return line.

Apparantly it's a very effective aerater, since I run my pump 24/7

Now that that's fixed, I may just leave things alone and see if my PH holds steady. 14-150 in a vinyl lined pool should be fine.

[waterbear]

Ben's sticky says you need to get PH low to induce carbon dioxide production.

Once carbon dioxide is present, I assume it's no longer measurable as part of the ALK test, and this is why we get the drop, right?

And if it's not gassed off, when PH increases due to aeration, carbon dioxide reverts back to CA, which is measurable, right?

Anyone know at what PH level carbon dioxide re-converts to CA? Waterbear?

Exactly right, except that the incease in pH is due to the CO2 being gassed off...as there is less carbonic acid the pH will rise but the buffer is in equalibrium so things shift as the pH rises..It takes a bit of time and patience to lower TA. pH determines the ratio of carbonic acid to carbonates/bicarbonates in the water.....lower pH means more carbonic acid and less measurabe TA. Higher pH is the reverse. If you remove the carbonic acid by gassing off the CO2 you have lowered the TA because you have less of the total buffer system in the water. As you you lower the carbonic acid the carbonate/bicarbonate try to reach a new equalibrim so they lower. The purpose of a buffer is to stabilze pH so the pH will rise as the equalibrium is reached. The net effect is a lower TA. In most pools the TA buffer will stabililize at a pH of around 8 so the addition of acid to keep the pH in range is still necessary.

[Rangeball]

Thanks Evan. I think I finally have my head wrapped around this.

I'm 100% certain my difficulties have been from aerating WHILE trying to lower PH. Doesn't work, for me.

Now that I made progress and can live with the result, I noticed I'm down about an inch of water from evaporation (and probably my splash out from the cannon balls), and dread having to refill soon.

The guy that runs our town's water plant was in my office a few days ago. I asked him if our alkalinity always runs high (320 when I tested, with a PH of 7.2). He said yes

I have a vinyl lined pool. If I followed Ben's "Run a high PH" page, I'll end up over 8 with an alk in the mid 250s.

Is this a problem at all if I just let the pool do what it wants? What would I be risking?

[Rangeball]

Tested again this noon just to see where I'm at. Haven't aerated since yesterday morning.

PH was 7.2.
Alk was between 130-40. I didn't wait long enough between the drops, and the 130 drop may have been enough. I'll call it 135

Since I'm this close to a good alk goal, the PH is still low and all my air leak issues seem resolved, I may go ahead and lower my ALK some more as I'm anticipating adding water again in a week or so. That way when I do hopefully I can keep alk under 200 and not worry about this much.

I'm out of acid. I guess the deciding factor will be how soon I go get some