High TA quesion

[plumgang]

I am trying to reduce the TA in my SALT WATER pool to 70. The level as
measured with the TF-100 test kit has flucuated between 150-230 since
I opened the pool a few weeks ago.

I added a LOT of muriatic acid and got the pH down to around 7.3...

1.) How long do I need to keep the pH this low before I'll see the TA
come down?

2.) Once TA comes down, what factors cause it to rise again? (I want
to avoid them if possible.)

3.) And how long after adding the muriatic acid do I need to wait before
testing both pH and TA?

I have a chemistry background so please don't hesitate to use technical
terms if it would help me understand better what I'm doing and looking
for.

Thank you...

 

[Bama Rambler]

Here's how it works. Adding acid lowers pH and TA. Because we have set constraints on what the pH level can and should be between we don't advocate adding acid to bring the TA down. What we do advise is to aerate the pool till the pH gets to somewhere around 7.6 to 7.8, because the affect of aeration is to raise pH but not TA, then to use acid to lower the pH which also lowers the TA. Then repeat that sequence of aeration/acid until the TA gets to where you want it to be. It's better to lower the TA to about where you think it should be then just adjust the pH till it reaches equilibrium.

 

[Butterfly]

Have you seen this article in pool school?

pool-school/lowering%20total%20alkalinity

 

[anonapersona]

You may want to test your fill water, that is typically the source of the TA in the pool. My tap water tested at 340 TA, so to keep my pool at 60 - 90 TA is a real chore when I am adding 1 or 2 inches a week for losses to evaporation.

You can lower TA fast or you can do it slowly. I've done it both ways and now slow is good enough for me. When the pool gets to 7.8, I measure TA and calculate the amount of acid to push pH to 7.2. Test pH every few days and when it gets back up again, retest TA, recalculate acid needed, and repeat.

When you lower the pH, the TA will go down a little, depending on how hard you hit it. You don't want to go below 6.8 pH for bad things can happen to equipment, best to aim for 7.0-7.2 if you are trying to go fast. To go fast, reduce pH, then aerate. I would turn on the waterfall and the spa blower.

The slow way is to adjust pH to 7.2 (lower of swimming level) and let it rise on it's own. I have a spillover spa and so there is a lot of regular aeration in my pool so even the slow method works eventually. Over time, if I am not adding much fill water, TA drops, maybe by less than 10 ppm in a week. Rainwater is low TA so that is a big effect in a year that normally has 55 inches of rain, mostly in winter.

If I must add fill water, TA will instead creep up. So I must add acid with every chlorine addition. TA has varied from 190 to 60 over time which is a huge difference. Really demands watching, but the action of pH is what clues me in that TA is high or low, I don't actually test it that often since I am doing it the slow way mostly.

Also, using chlorine tablets in the automatic chlorinator really works to reduce TA. The few times I have hit TA 60 was after a long vacation with a lot of tablets used. I am still running on the load from the last trip and I can tell that since the pH is stable at 7.6 and so there are still tablets in the system. The day I find 7.8 or 7.9 pH, I will know that the tablets are gone and I need to do a full test to see where we are with TA so I can use the right amount of acid to control the pH as it marches toward 8.0+.

 

[plumgang]

Thank you for the info....the pH stayed down at 7.3 today...I turned the water jet so it breaks the surface with bubbles
and have started using the SWG to chlorinate the pool again, so the pH should rebound...I'll just keep checking pH and
once it gets to 7.8 again, I'll add muriatic acid to lower it to 7.3. Sounds like TA isn't going anywhere fast...

 

[JamesW]

If your calcium is high, then you will want to lower the pH back to 7.2 when it gets to 7.4 or 7.5. If your calcium is lower, then you can wait a bit longer if you want (pH of 7.6 to 7.8).