pH looks odd

[Rental Pool]

My TA is 70. My pH shows 8.0, yet 1 drop of R-0005 takes it to 7.4. This is a 20k gallon pool. Do I add acid or not?

 

[duraleigh]

What does PoolMath tell you?

 

[Rental Pool]

I know poolmath says add acid, but I'm questioning how 1 drop can drop the pH from 8 to 7.4.

 

[bdavis466]

Your pH probably isn't as high as you think it is. The color ranges above 7.8 are pretty hard to distinguish from one another. Since you have the acid demand test and you are sure the pH in the block is 7.4, you can run the numbers backward to see what your pH was before the acid demand reagent. This will at least give you an idea of what the color looks like at the higher pH ranges.

I find it easier to go with Pool Math though.

 

[Rental Pool]

My concern is that the more acid I add the lower the TA goes. How much lower than 70 is acceptable?

 

[bdavis466]

50 is the lower limit. The good news is the lower your TA gets, the slower your pH will rise. Hopefully you'll be able to find a stable point where your acid demand significantly decreases.

 

[Rental Pool]

That feels more comfortable. Thank you. I'll keep adding acid.