TA drop after adding soda ash

[archer636]

My pH was under 7, so I added 2-3 pounds of soda ash. The pH went up to 7.6- however the TA dropped from 80 to 30! does that make sense at all?

 

[Richard320]

It can't.

Repeat the test. Make sure you didn't grab the wrong reagent when testing, too.

 

[JamesW]

If your pH was below 7, the starting TA was probably not 80. For a pH below 7, a TA of 30 makes more sense.

Most likely, you had testing errors before or after adding the pH increaser.

What is the history of the chemistry?

If your pH got below 7, it implies that you let the chemistry get away from you by not monitoring it enough.

Sounds like a lot of tab use with insufficient testing.

 

[archer636]

If your pH was below 7, the starting TA was probably not 80. For a pH below 7, a TA of 30 makes more sense.

Most likely, you had testing errors before or after adding the pH increaser.

What is the history of the chemistry?

If your pH got below 7, it implies that you let the chemistry get away from you by not monitoring it enough.

Sounds like a lot of tab use with insufficient testing.

in the past I have been using liquid chlorine and it has been stable- so I don't test that often (except for FC). Recently I had to use more tabs because of frequent travel.
would you recommend adding a whole bunch of baking soda?? I have never seen the TA this low.

 

[JamesW]

If you raise the TA to about 80, the pH should remain stable. However, the CYA also needs to be monitored as tabs add a lot of CYA.

Assuming a starting TA of 80, you would have to add about 345 ounces (about (49) 7ounces tabs or 21 lbs) of trichlor to lower the TA to 20. Adding 2.5 lbs of sodium carbonate, would raise the TA by 10 to 30 ppm, which is where you are now.

345 ounces of trichlor would add 84 ppm of chlorine, which would be about 28 days at 3 ppm estimated daily fc demand.

345 ounces of trichlor would also raise the CYA by 51 ppm, which should be checked to see where you are now.