Muriatic Acid additions with Borates

[tcm0116]

Hi all!

My pool was completed last August, and I spent the last month of the swimming season getting the hang if the TFP method.

Over the winter, I read about the benefits of borates and decided to take the plunge. I only had to add acid every week or two, and all seemed well.

Fast forward to now, the beginning of swimming season. The water temperature is close to 80, and I've been having to add acid at least once a week. However, when re-testing the pH a little while after adding acid, I seem to always overshoot. Because of this, I've found that only using maybe around of 65% of the acid recommended by the calculator gives me the desired result. Here's an example from this afternoon:

Results from testing at 5:30 pm:

Temp: 77.1
FC: 6.0
CC: 0
PH: 7.9
TA: 80
CH: 350
CYA: 80
Salt: 3200
Borates: 40 (my best guess based on the test strip)

The calculator said to add 50 oz of acid to get to a pH of 7.6. I added 32 oz instead and retested 30 minutes later and got a pH of 7.6.

Any idea why the calculator is so far off?

Thanks!

 

[Saturn94]

It could be your pool is actually less than 23k gal.

 

[tcm0116]

I thought about that, but I didn't seem to overshoot before I added the borates. Playing with the numbers in the calculator, my pool would have to be more like 15k gallons for 32 oz of acid to drop the pH from 7.9 to 7.6 with the test results as listed above. However, if I lower the borates to 20 with 23k gallons, then it says to add 32 oz of acid.

I'm using the Lamott test strips, which are not super accurate, but the results they provide make sense. I added the borax based on the math provided in this forum and the test strips appeared to agree. Since then, we've had a ton of rain, and I've had to add three bags of salt, so a borate level of around 40 is reasonable.

At this point it still seems like there's an issue with the calculator, but I would think other people would be complaining, so I must be missing something. Any other ideas?

 

[tcm0116]

I retested the CYA level and realized that it was actually down to 50 from 80. Based on that, I figured that the Borate level was actually lower than I thought, so I went ahead and added enough borax to go from 30 to 50. The next time I need to add acid, I'll go by what the calculator says, and if I overshoot again, I can use that to figure out how much more borax to add. Since all of the other tests are much more accurate than the borates strips, that's probably an even better method for determining the level of the borates.