Quote Originally Posted by chem geek View Post
If the CYA dropped from 100 to 30 ppm, then that 70 ppm could get converted into around 20-25 ppm ammonia that would require roughly 200 ppm FC to get rid of. That's worst-case, but is an extraordinary amount of chlorine required to be cumulatively added.
So if my math is right (and I'm not at all sure it is), 200ppm FC calculates out to roughly 70 gallons of bleach in my size pool (19,400 gal). I have used about 75 already, so hopefully I will be done soon. Unless of course the scenario is really much worse and my CYA was much higher at the end of last season. I know when I first discovered how high it was it was over 150, but we did drain some and dilute and I'm pretty sure I got it down close to 100 - but I know I was still having to dilute my sample to be able to test it, so it may have been higher. Ugh! After putting all this into it, just not too sure I'm ready to drain and dilute. We would be hiring someone to do that since i am not willing to risk messing my liner up doing it ourselves, and that would surely be more costly! Thank goodness for Sam's and cartons of big jugs of bleach!!