When the media in my reactor "dwindles down" I like to clean the reactor, circulation pump, and top off the media.
I try to rinse the media in a collander to remove small particles because smaller particles like sand may interfer with the circulation pump and cut down on the efficiency of the reactor.
It partly depends on the media you use. Some dissolves cleaner than others. ARM dissolves fairly clean and I just top it off, but will probably clean the reactor once a year to get rid of any excess fine particles. I have heard that some of the other media tend to dissolve into a goop and the reactor has to be completely cleaned each time. If it looks like you are accumulating a lot of muck in the bottom of the reactor, you're probably better of cleaning it to be safe.
