Why did my TA drop?

fscott

Active member
Feb 19, 2010
25
San Diego, CA
Hi pool lovers!

We've been managing my pool with BBB for 9 months and everything's been hunky-dory until today.

I test the pool once a week and pH usually rises a bit while FC drops. Add the appropriate amount of muriatic acid and bleach and it's all good.

Typical previous readings:
FC 3-7
CC 0
TA 80-90
CH 400-600
pH 7.2-7.8
CYA 30-50
Borates 50

Today's readings:
FC 5.5
CC 0
TA 20
CH 600
pH <6.8 (it's quite yellow!! I'm guessing around pH 6.2?)
CYA (ran out of reagent...it's in the mail)
Borates 50

Now to the questions:

Were the **** did the TA go? This has never happened before so I'm very confused. Asked the hubby and he swears he didn't add any acid to the pool THINKING it was chlorine...

Do I just need to add a gut load of baking soda? 11 pounds by the pool calculator??? Is it even possible that this could be right?

Thanks in advance!
Fiona
 

Butterfly

TFP Expert
LifeTime Supporter
May 30, 2007
10,045
South Carolina
Hi Fiona,

fscott said:
We've been managing my pool with BBB for 9 months and everything's been hunky-dory until today.
:goodjob:

My suggestion is that you take your time and run your tests again to confirm before making any changes.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
I agree that you should confirm your readings, but having both TA and pH low is consistent with having acid added to your pool. To go from your starting TA of, say, 80 ppm to 20 ppm, that's over 20 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 11,000 gallons. The pH would get to as low as 5.8 except that there should be carbon dioxide outgassing so might be at around 6.5 or so.

If you verify the readings, then if the TA is truly 20 ppm then you would add about 15 cups (a little over 9 pounds) of baking soda to get to 80 ppm which is a reasonable level to prevent the pH from rising too much though with any such large move try adding half, mix with the pump running for an hour, then re-measure to make sure you are on track.
 

fscott

Active member
Feb 19, 2010
25
San Diego, CA
Crisis averted!

A second pool sample was completely normal: pH 7.5 and TA 80....it's a mystery....

Thanks for the advice -as usual TFP forum never lets me down.

Over and out.
Fiona