You absolutely must use freshwater, in your sink, when cleaning your screen once a week. If your weekly cleaning gets delayed, at the very least turn the pump off and pour RODI over the screen to kill the pods. Otherwise the pods start growing underneath, eating the algae, then falling off into your water. You will not see the holes they make unless the algae is very thin. It becomes an issue of the scrubber not removing as much nitrate and phosphate, because the pods eat the algae you've grown, and then re-introduce the nutrients back into the water. FW of course, kills the pods. SW does not. So use FW weekly. And don't worry about getting rid of all the pods; you won't. The next day there will be millions more.