I have a tiny (140 gallon) hot tub that uses a Silver Ion sanitation system (explained by chemgeek here).
The silver needs an oxidizer to work correctly, and the manual instructs weekly additions of Dichlor -or- MPS. They specifically say the use of liquid chlorine will not work with the Silver system properly. I've been using Di-Chlor because it's what I have on hand, but as you can imagine it has increased the CYA level to 100+. So, does that high CYA level change the oxidation properties of FC in addition to sanitation?
I'm asking more out of curiosity than anything else - the tub is so small it's not a problem to replace a bit of water or use MPS exclusively.