Thanks for all the responses.

I have been trying to keep in line with the recommended chlorine levels since finding this forum. CYA is about 70 as of 3 weeks ago. Vinyl pool, 24K. Ph is 7.8. I've been using liquid chlorine to keep it at 5 (except for a week I had to go out of town).

So things are not bad, but when I end up out of town for a week here and there, and I was wondering if the phos free stuff I have is useful for those periods, or if I should toss it.