I only use the pad when stirring or siphoning out my sand -- just to catch detritus. Usually take it out the next day, rinse thoroughly, and hang to dry until the next time. Anywhere, including on such a pad, where you collect detritus can produce a lot of nitrate over time. You'll likely want to remove the bioballs over time as well, because they too can produce nitrate unless you keep them very clean and/or submerged at all times. I still have mine in, but I'll start removing them if I ever see nitrates above about 2.5ppm. Currently 0.0ppm, so I'm not worrying about it...