Copied and pasted from another post...hoping for some input on this.
... a couple of weeks ago I set up a 5 gal. tank. The 5 gal. tank filter uses the same model filter cartridge as my 10 gal. tank. I took the the old filter cartridge from the 10 gal. and put it into the 5 gal. and put the brand new filter cartridge into the already up and running (3 mo. old) 10 gal. tank.
Did I mess up my 10 gal. by doing this? At any time is it appropriate to change to a new, unused filter cartridge? Should I never change to a new cartridge, just simply rinse and reuse the old one?
There is a secondary type of media in the filter, more like a nylon type filter (kind of like a pot scrubber). This has not been changed and I have read in the manual that came with the filter to never wash it. I haven't.