8lbs of baking soda but only increased TA from 30 to 50?

[BruceA]

13,500 gal pool, no problematic symptoms other than always creeping PH (I try to keep it just in the light orange/peach colors, not pink or god forbid red).

According to the pool calc I should have only needed 6lbs to hit my target of 70. Came in 4lb boxes so just used both of them fully to get it a little bit higher which I figured would be fine. On retest a week later only bumped 20 ppm?

 

[Richard320]

13,500 gal pool, no problematic symptoms other than always creeping PH (I try to keep it just in the light orange/peach colors, not pink or god forbid red).

According to the pool calc I should have only needed 6lbs to hit my target of 70. Came in 4lb boxes so just used both of them fully to get it a little bit higher which I figured would be fine. On retest a week later only bumped 20 ppm?

Did you add any acid in the interval? Adding acid to lower pH also lowers TA.

 

[BruceA]

Sure, but not that much 1 qt tops maybe.

 

[Richard320]

It looks like the baking soda you added would have pushed TA from 40 to 80ish. The acid would cancel out 9 of that, it would likely show up as 70, which doesn't quite tally with your 20 ppm rise. Still, that's only off by one drop. That's within the tolerance given in Extended Test Kit Directions,

• The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.

Aside from that. it could be a bunch of things, none of which are that big a deal.
1) Static electricity on the tip of the reagent during the first test could have made it read artificially high
2) The pool is bigger than you think
3) Sample size was off a little bit or you miscounted

I wouldn't worry about it, just store the information and pay attention. If you consistently undershoot, you'll know the pool is bigger than you think. If it was a one-time fluke, it was probably an error counting drops.

 

[BruceA]

Obviously I tried to avoid all of those:
1) I wiped the tip with a damp cloth each time (before, after and retest) using the mixer I got with the kit
2) Everything else lines up well with this estimate (admittedly still its an estimate)
3) I hope I can count to 5... don't even need to remove my shoes
but yea like you say, chalk it up to experience and go get some more baking soda. Will try another 4-5 pounds that ought to get me to goal around 80-90 and then test again. Thanks for the advice!