TA suddenly dropping...

[Freakaloin]

We have a 14 month old pool and I have been successfully doing BBB approximately 11 months. Up until about a month ago TA was relatively stable around 100. In 10 months I probably added baking soda 2-3 times. Also until a month ago, PH was constantly rising to where I needed to add MA every 2-3 days. Suddenly PH was more stable and TA began dropping. At one point it dropped to 10. Now, I'll raise TA up to 110ish and it drops to 60 in 4 days. PH is back to rising fast...

What is up?

FC 3
PH 7.4
TA 60 (100 on Saturday)
CH 350
CYA 40

 

[pwrstrk]

Have you've been topping pool off ? What's the TA of your fill water ? ?

 

[Freakaloin]

It auto fills...

 

[Freakaloin]

I just tested tap water... TA=140

 

[JamesW]

Are you using trichlor tabs?

 

[Freakaloin]

No I'm doing BBB...

 

[JamesW]

Dropping TA has to be from added acid, or something acidic.

How much acid have you added?

What are you lowering the pH to when adding acid?

 

[Freakaloin]

I try to keep it between 7.8 and 7.4. I usually add around 30 ounces every 2-3 days. I used to measure it out but lately I have just estimated. I'll start doing everything by the book until I figure what's going on...

 

[JamesW]

Try keeping the pH at about 7.8. At 7.9, lower the pH to 7.8, and not lower. Keep the TA wherever it needs to be to keep the pH at 7.8.

If the pH rises above 7.8, lowering it to 7.8 will slightly lower the TA and eventually stop all/most pH rise.

If the pH keeps going below 7.8, then slightly raise the TA until the pH stabilizes at 7.8.

If the pH is holding steady at 7.8, then leave the TA where it is.

What is the water temperature?

 

[Patrick_B]

If you have high TA fill water such as yours, there really should never be a need for baking soda. James is correct, you must add something acid to break down TA, so you were pushing the pH down too far too often to break down the TA like that.