Can't keep TA above 60

[eemueller]

Help! It seems that the TA in my pool wants to be at 60. I can dump in baking soda, and get it back to 80, but within a day or two it drops back to 60 and stays there. I have very little surface disruption from the returns, so short of aiming them down, I'm out of ideas. All my other numbers are fine. Thanks in advance...

 

[YippeeSkippy]

Can you provide a full set of test results, in particular your pH?

 

[chem geek]

Aeration does not change TA. TA only gets lowered from some kind of acid addition. That can be from adding acid or using net acidic sources of chlorine such as Trichlor or Dichlor. Non-chlorine shock (MPS) is also acidic.

Make sure you wipe your dropper tip with a damp cloth to get rid of static electricity every time you do the test. Also make sure to hold the bottle upright to form well developed drops that hang before falling. Don't rush the test so don't squirt out the drops.

 

[eemueller]

This morning, the pH was 7.5, TA 60, TC 4.0, CYA 70, Calcium hardness 300, temp 82 deg F.

- - - Updated - - -

Chem Geek, There is acid added into the return line to counter the pH increase from the SWG. I use a 50/50 solution of muriatic & water that is pumped directly into the line from a 15 gal tank. I'm going to redo the test, doing the things you suggested.

 

[chem geek]

So that makes sense. Adding acid lowers TA. You are in the acid+bicarbonate vicious cycle. You can lessen that by maintaining a lower TA (say 60 ppm) and having a higher pH target (say 7.8). If you settle in on a particularly low TA that has your saturation index get low in spite of your higher pH target, you can compensate by raising your CH level. PoolMath calculates the saturation index for you, but get your pH more stable first. Finally, some people with SWG pools use 50 ppm Borates to help control the rate of pH rise.

 

[eemueller]

How do I get the pH more stable, short of adding borates? When I entered my numbers in PoolMath, my saturation was -.29, which falls in the acceptable range. To increase the TA, it said to add baking soda, which I already know to do. I thought I wanted my pH to be 7.5-7.6 and no higher. If I turn off the acid pump, and let the SWG run, the pH will go past 8, and I'm sure I don't want that. I'm running the SWG at the lowest level possible to keep the TC at 4.

 

[pooldv]

Let the TA stay at 60 or even 50 and see how your PH acts. If PH stabilizes then let TA stay there.