Alkalinity Info.

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.

Alkalinity Info.

Postby doug30 » Sun 01 Jul, 2007 22:47

Hi all, first post here.

Another Alkalinity question for the pros.
We have a 30' above ground.
Filled with well (hard ) water last fall.
Prepped it for winter and it seemed to do quite well.
This spring did the initial treatments and started the chemicals.
The water has been great- clean and sparkly.
However, I've noticed my TA hovering around the 180 range.
PH seems good at 7.2- 7.5 range.

So about a month ago, I added approx. 1 gal. M.A.
Didn't seem to drop after a day or 2.
So I waited a couple weeks and added another 1/2 gal.
Again, didn't see much of a change.
Yesterday, I added another 1/2 gal. but this time, I poured it in one spot out of a 5 gallon buckete diluted with water.
(The other times I spread it aroud the pool)
I also (after reading these posts :wink: ) aerated by turning my inlet nozzle up to create bubbles.
Now I've noticed TA dropped "slightly" but also my PH dropped.
Soooooo, should I continue adding MA and aerating?
This makes about 2 gallons I've used.
Also how long do you typically aerate the water.

Thanks in advance. Great site!

chem geek
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Postby chem geek » Mon 02 Jul, 2007 00:34

You probably didn't notice the pH dropping before because your pool has a tendency to rise in pH due to the high TA. So any drop in pH just accelerated the outgassing of carbon dioxide causing the pH to go back up. The TA would have dropped with this combo, but not enough to be measurable.

Follow the procedure in this post to lower your TA. You will notice that not only is there aeration, but you also add enough acid to lower the pH to the next lowest reading on your pH test kit (7.0 or 7.2 depending on the kit). So aerating makes the pH go up, you add acid to keep it down, and if you do this with lots of aeration and not letting the pH go up too much (i.e. stay on top of adding acid), then the TA will go down rather quickly. You should be able to get your TA down within a day or two.

How you add the acid does not matter very much. There is a "slug" theory that says adding the acid quickly in one place is more effective at lowering TA, but that's only very slightly true. It does not drive off carbon dioxide in that local region, but it does make that local region more acidic briefly and during that time there is more outgassing at the surface -- it's just a rather small incremental effect. Lowering the pH of the entire pool and then doing lots of aeration while adding acid to keep the pH low is MUCH more effective at lowering the TA.

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