High TA fill water and an SWG

[jsternberg]

We will be building a pool soon and have decided to go with an SWG. I tested the calcium hardness and TA of water coming out of the outside faucet and got:

CH 200 ppm
TA 120 ppm

I saw that in the Water Balance for SWGs that I should aim for a TA of 60-80 ppm. My fill water is obviously higher than this so I'm going to need to go through Lower Total Alkalinity.

But, there's something I'm unclear about and I wanted to check my understanding. When my pH becomes too high, I am supposed to add muriatic acid to lower the pH regardless of the TA. With my TA being too high from the fill water, the pH is going to rise more quickly. The pH rising quickly is caused by aeration in the SWG. If my pH were to get too high, then I need to add muriatic acid to get the pH back down. This has a side effect of also lowering the TA of the water which means I need to use muriatic acid less frequently in the future.

To me, it seems like the process is just "add muriatic acid when the pH gets too high". Is there anything else to the process? It seems that high TA itself doesn't cause a problem so I can have a high TA, use the pool, and then just keep close track of the pH so I can correct it. I'm hoping it is this simple and I'm not missing anything.

Thanks for the help. I want to make sure I'm ready for the water chemistry before we fill the pool.

 

[Texas Splash]

What you should find as you get the pool operational is that you will first focus on the pH keeping that managed around 7.8. If you need to lower the TA, then the acid will lower both a little. Eventually, you expect to see that pH stabilize around 7.7-7.8. At that point, the TA may be 60, 70, 80, or 90. Main point is you want the pH to remain fairly constant. For salt pools, that typically is around 7.7-7.8. Each pool is different. Now once they stabilize, it's inevitable you will need to add a little acid to manage the pH, but those amounts shouldn't have a huge impact on the TA at one time. Over a longer period it might at which point you'll add a little baking soda - usually when the TA hits 50. But those applications should be manageable without huge swings either way.

 

[mknauss]

The pH rising quickly is caused by aeration in the SWG.

Not true. The pH is higher within the cell itself, but does not effect overall pH levels in an appreciable way.
Your fill water elevated TA will drive your pH higher. But it will be very manageable.

 

[ajw22]

TA is the least important chemical you measure. A low TA below 50 can cause problems with pH stability. There is no too high TA that requires immediate action. As you observed a high TA will cause pH to rise, which will cause pH to be lowered with acid, which will also cause TA to be lowered. So high TA tends to be self limiting.

High TA can contribute to longer term problems with high CSI and scaling. But you have months after you fill your pool to deal with those issues.

When you fill your pool focus on your FC and pH. Let the TA be whatever it is. After a few weeks you can start fine tuning your water chemistry and seeing what TA your pool is happy with. When you have high TA fill water your TA will never stay low since everytime you add fill water to replace evaporation it will spike your TA up.

TA - Further Reading

www.troublefreepool.com