Time to replace sand?

[jonno]

The pool failed the overnight test. This morning FC = 0.5 TC = 5.5, pH = 7.2, TA = 190.
Thanks for the information about lowering the TA Ben. My return is ruffling the surface and I'll pick up some muriactic acid today. I'll also stock up on bleach.

Ben - can you clarify your instructions:
1. Add 6 gallons of bleach nightly until I get 15ppm the next evening - is that FC or TC?
2. Continue that way until the CC is below 1ppm - does that mean that FC and TC should be within 1 ppm of each other?
3. Get that TA down with muriatic acid until pH is 6.8. Wait for pH to climb above 7.0, then add another dose of muriatic acid - how long should i wait between tests? how much muriatic acid should I add for each dose? 1 cup for a 26K gal pool? Follow instructions on muriatic acid container?

Watermom (and Janet) - the priority in your instructions seems to be to get the chlorine to 25 and keep it there. The 17 gallons of bleach I added last night only got the FC to 4.0 and this morning it has dropped to 0.5. Here are my questions on your instructions:
1. You advised me to test as many times a day as possible and bring the cl back up to 25 each time (so the FC = 25 right?). I'll add another 17 gallons this morning, but how long should I wait after adding the bleach to see if I've reached 25? If not, I should add more bleach immediately - right?
2. You said to keep pH above 7.2, but Ben says to follow the steps lower the TA - should I do that now or wait until the FC passes the overnight test by holding within 1ppm of 25?