IME the good microbacter is both in the water and in the filter(s) if you tank is set up and cycled, you should have no problems maintaining good water quality even if you treat w/ meds. I may be way off here but it has worked for me this way. Also in my 20g the water changes are a bit more frequent, especially with the little filter I use. (nitrate builds up) Hope this helped. Be sure to wash out your sponge with saltwater, not fresh. If you do treat with copper you may want to consider getting a new sponge and definately new carbon, when the copper is gone. Better safe than sorry.
[ July 20, 2001: Message edited by: mal ]