Is there a certain window of time

[Rangeball]

I'll report back in the morning.

Looks like the rain may be re-grouping and we may get some after all. I won't hold my breath

From what I understood in the "lower your alk" sticky, if you don't gas of the C2O when the PH is down it can convert back and measurable alk goes back up with the PH.

I'm hoping that my previous aeration efforts were just inadequate. We'll see.

[Rangeball]

Got up early, grabbed my test kit and headed to the pool. It never did rain.

Pool had been aerating since noon yesterday.

Tested-

PH- 7.6, only dropped a bit.
Alk- 180, only dropped a bit.

I had expected a much bigger PH drop from the amount of acid I put in. I also expected the alk to be much lower.

I thought about this for awhile, and came up with a hypothesis.

In the "lower your alk" sticky thread, a poster asked if you could start aerating as soon as you add the acid. Ben responded stating it wouldn't work until the PH dropped but it probably wouldn't make a difference either way.

I'm wondering if thats correct.

If aeration increases PH while gassing off carbon dioxide to keep alk down, adding acid and immediately aerating seems counter-productive. My pool has been constantly aerated either by young swimmers or air in my return line. In looking back, the only time I got a good PH drop was when I had the air leak stopped and was getting good flow with no aeration and low swimming load.

I turned off the sump pump aeration, and added more acid, but didn't have enough to get PH as low as I need. I'll get more some time today, retest my PH and add more. I'll then try to hold the kids off from swimming tonight, retest tomorrow morning and hopefully begin aerating then.

Make any sense?

If this doesn't do it, I guess I'll be forced to live with high alkalinity and rapidly escalating PH levels

[Tredge]

Interesting thoughts.
Maybe your aeration isnt enough? Or maybe you are not maintaining the PH at a low enough level for long enough....since it tends to creep up so quickly maybe its demanding more attention?

My pool is filled and I have the High TA also so I begin my aeration process tonight.

I should also have good numbers today so we can compare notes.

[Rangeball]

Interesting thoughts.
Maybe your aeration isnt enough? Or maybe you are not maintaining the PH at a low enough level for long enough....since it tends to creep up so quickly maybe its demanding more attention?

How long is it recommended to let the water circulate before testing PH? I gave mine a good 19 hours of circulation before testing PH. The water probably turned over 3-4 times, so it should be plenty mixed. I'm thinking the PH was dropping but being offset by the aeration so it stayed more or less stable as the end result.

I added acid this morning. I'll test ph again at noon to see what it did. This will be 5 hours later. If PH is low enough, I'll check alk. If not, I'll add more acid. I'm starting to run low on my alk reagent, and although it only costs $1.69 for another bottle with free shipping, it's a flat $6.99 "handling" fee.

My pool is filled and I have the High TA also so I begin my aeration process tonight.

I should also have good numbers today so we can compare notes.

Sounds great

[waterbear]

But is it the aerating that's lowering the alk, or the acid?
TA is a measure of the carbonic acid/bicarbonate/carbonate buffer system in the water. Only the carbonate/bicarbonate part of it is measurable by testing. When you lower pH you shift the amounts of the three components to more carbonic acid and less of the other two. The amount of the buffer is unchanged. When you aerate you drive off some of the carbon dioxide (carbonic acid is just carbon dioxide gas dissolved in water....think club soda, exactly the same thing. Aerating...think shaking the bottle of club soda to make it go flat...exactly the same thing).
By driveing off the carbon dioxide you:
1 lower the amount of the buffer system in the water
2 this causes the pH to rise since there is a higher ratio of bicarbonate/carbonate to carbonic acid and less acid means higher pH (simplified a bit but essentially true)
3. once the pH rises the buffer system reaches a new equilibrium point and there will be less meaurable carbonates/bicarbonates in the water....you have now succesfully lowered the TA!

In other words, is it-

1- PH is 8, Alk is 200. Add acid, PH drops to 7.2, alk at 200, aerate, alk drops while ph rises. Keep lower PH and aerating until alk lowers to where you want it then stop.

2- PH is 8, Alk is 200. Add acid, PH drops to 7.2, alk drops to 140. Aerate, PH rises but alk stays at 140 because carbon dioxide is gassing off from aeration. Continue to drop PH and aerate until you get alk where you want it.

I had understood it to be #2. However, My PH is dropping, but alk isn't. And for some reason Alk increases along with PH when aerating.
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.

Somethings not right

Hope this doesn't confuse you too much!

[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!