Thanks,

I have a Taylor K-2005 which can test for free and total chlorine, so I can calculate combined. And you are right, I've never really had the need to shock, except during the late winter. The days get warm enough to cause problems, but the water doesn't get warm enough to generate chlorine. I usually end up with a bloom every year about the end of January to mid-February.

So I will shock every so often during this time to keep the water clear.

Is there an advantage to using the non-chlorine shock? Should I be using a non-chlorine shock? or is it just person preference?