Had a t-15 in my 14,400 gal. pool that went out a couple of weeks ago. I normally had no trouble leaving it at 60% for my runtime during the day and it maintaining a reasonable FC level. Today, after having my new t-9, been in for some time but hasn't been checked daily, running for a few days with the same run times at 60%, my FC was at 12.5%. Looks like I'm going to have to work at dialing this one back. Which is a good thing. Bad thing is I'll be unable to check it next week so I'll just have to set it and hope for the best. Probably going for 40% at the same 10 hour runtime, and see what numbers it keeps.
I guess the old cell was just that bad.