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:
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?