JackVa1,
If there's still bromine in it, don't remove it. And if it's the sales person who told you to change it every month then they're just trying to generate some revenue!
Personally, I haven't bought a bromine cartridge for my frog system in a couple of years. I have the early version of the King Technology cartridges that have a removable top. When it gets low, I just refill the cartridge with 1" bromine tablets. The cartridge is a little discolored but other than that, it's working fine.
Anyway, replace it only when it's near empty and save yourself some $$$
Phil