My tanks finnaly up and running and im loving it. i have 2 angelfish and a pleco. its a 20 gal planted but its time to change the filter.... i think. its been a little over a month so im guessing its time to change it. but whats the best way my filter only has one slot for media so how to i go about switching them out do i just stick the new one in with the old for a day or so?