Total Alkalinity Falling

[RVbiker]

Last fall I drained the pool because of high CYA. I refilled the pool with 11,000 gallons according to the water meter but left it about three inches below full thinking the winter rains would complete the fill. I decided to add borates(20 Mule Team) after the refill and had to readjust them and the CYA once the pool was filled. I followed the procedure prior to adding borates and afterwards as recommended here.

Prior to refilling the only chemicals I had add was chlorine and about 30 oz. of MA once a week. But now I find the TA falling. This past week I added baking soda to bring the TA from 50 to 80. Here in Arizona the evaporation is quite high so I'm adding a lot of water weekly. The municipal water supply has a ph of about 8.2 and a TA of 110. I can understand why the ph rises but not the TA falling as it does. I have always kept the TA between 80 and 90 and had the TA as high as 100 but I'm now thinking that perhaps I should bring the TA to perhaps 120 where it may be more sustainable.

Any thoughts would be helpful. Thanks.

The pool chemistry is as follows:

Cl - 5.0
CYA - about 50
Borates - 50
ph - 7.6
TA - 80
Calcium - 280

 

[Texas Splash]

Using the PoolMath tool, your CSI is currently at -0.2 (Balanced). Since water in your area is generally hard, and CH skyrockets quickly, I'd leave the TA alone for now and simply watch your CSI in PoolMath. That slightly negative CSI should help to control potential scale.

 

[JamesW]

What chlorine are you using?

 

[RVbiker]

What chlorine are you using?

I'm using HDX Chorinating liquid 10%.

 

[Texas Splash]

I'm using HDX Chorinating liquid 10%.

You should be fine then. I think James was asking in case you were using tabs/pucks which are acidic by nature and can pull-down the TA.

 

[JamesW]

TA can't drop by itself. Something acidic has to be being added if the TA is dropping.

 

[RVbiker]

Using the PoolMath tool, your CSI is currently at -0.2 (Balanced). Since water in your area is generally hard, and CH skyrockets quickly, I'd leave the TA alone for now and simply watch your CSI in PoolMath. That slightly negative CSI should help to control potential scale.

Thanks Pat.
When I bought the house about a year and a half ago the pool had a white deposit around the water line. Before I refilled I scrubbed most of it off and haven't seen a reoccurance of it since.

Maybe I'm thinking about this wrong but I thought with a high TA of the refill water it would help keep the pool TA high. Perhaps I should be thinking that TA is a condition rather than an additive.

 

[RVbiker]

TA can't drop by itself. Something acidic has to be being added if the TA is dropping.

I would think if that was the case my ph would dive as well but it has been behaving as it always have. It's monsoon season here and we've have recent storms that have deposited debris in the pool overnight but I usually clean it the next day.

Also, I recently had to replace my Hayward VS pump and replace it with a Pentair VSF pump. It was at least two days before it was replace and the pool was begining to cloud up but once the pump was replaced the pool cleared up nicely and the chemistry returned to normal.

- - - Updated - - -

 

[JamesW]

Rain has low TA, so that can account for some TA loss.

Also, if you get a lot of rain while the pump is off, rain water can stay on top of the pool water and, if the sample is taken from the top water, the test can be inaccurate.

 

[RVbiker]

Thanks for all your replies. I think I'm going to watch the TA for a while to see where it goes. My concern is I feel like I'm getting into an acid/alkaline seesaw where on day I'm adding acid to correct ph and the next adding baking soda to correct TA which seems contradictory. Hopefully things will settle down.

 

[ajw22]

I'm adding acid to correct ph .

At what PH do you add how nuch MA to lower it to what PH?

 

[RVbiker]

At what PH do you add how nuch MA to lower it to what PH?

Allen, I add acid when the ph gets to about 7.8 and enough to get to 7.2 where it seems 7.4 is the sweet spot to get the best sanitation from the chlorine.

 

[ajw22]

Allen, I add acid when the ph gets to about 7.8 and enough to get to 7.2 where it seems 7.4 is the sweet spot to get the best sanitation from the chlorine.

Lowering PH to 7.2 is why you are dropping your TA so much. The lower you drop your PH, the more you drop your TA. Lower the PH to 7.6 when it gets to 8 will keep your TA more stable.

I have not heard of any connection between PH level and chlorine sanitation.

 

[mknauss]

I have not heard of any connection between PH level and chlorine sanitation.

There is a slight effect on chlorine effectiveness at lower pH. CYA in your pool water makes it negligible.

Review Pool Water Chemistry

 

[RVbiker]

Lowering PH to 7.2 is why you are dropping your TA so much. The lower you drop your PH, the more you drop your TA. Lower the PH to 7.6 when it gets to 8 will keep your TA more stable.

I have not heard of any connection between PH level and chlorine sanitation.

Allen, I'm aware that adding acid will drop TA. My concern is why TA is dropping by itself so when I do add acid to correct ph it drops TA further resulting in the addition of an alkaline(baking soda). I just don't know the mechanism why the TA is dropping on its own and I haven't notice the ph dropping abnormally.

 

[ajw22]

Allen, I'm aware that adding acid will drop TA. My concern is why TA is dropping by itself so when I do add acid to correct ph it drops TA further resulting in the addition of an alkaline(baking soda). I just don't know the mechanism why the TA is dropping on its own and I haven't notice the ph dropping abnormally.

But the way you add acid can have a small or large impact on your TA.

Are you sure you don't have testing variances? Have you used consistent testing techniques? How old is your test kit? Do you wipe the tip between each drop? Do you hold the bottle verically and let the drop fall off the tip?

 

[mknauss]

TA cannot drop on its own. Either an acid is being put into the pool (trichlor, dichlor 'shock', muriatic acid) or fill water has very low TA, which I am pretty sure yours does not.

 

[RVbiker]

TA cannot drop on its own. Either an acid is being put into the pool (trichlor, dichlor 'shock', muriatic acid) or fill water has very low TA, which I am pretty sure yours does not.

That's what I thought and the reason why I tested the the fill water TA which is 110 which is far from acidic. If acid is being introduced it should be keeping my ph stable which it is not.

 

[Texas Splash]

If acid is being introduced it should be keeping my ph stable which it is not.

The only other consideration I haven't seen in this discussion is possible aeration. If you have any aeration that would increase your pH while leaving the TA low. Those monsoons might do that a little. Your sig doesn't show any aeration features, but if you do have a fountain, bubblers, etc, those will drive-up the pH. Just a thought.

Have a nice weekend!

 

[RVbiker]

The only other consideration I haven't seen in this discussion is possible aeration. If you have any aeration that would increase your pH while leaving the TA low. Those monsoons might do that a little. Your sig doesn't show any aeration features, but if you do have a fountain, bubblers, etc, those will drive-up the pH. Just a thought.

Have a nice weekend!

Pat, that's a good thought. I have a waterfall and small fountain which I will add to my signature but none have been in use this season.. Thanks.