I clean out the pre filter weekly, and take apart and clean out the entire filter once a month. There are I think 6 trays inside, and it depends on what you have in the trays as to a cleaning schedule.That Oase is a nice unit!
The pond filter I'm using is bio beads only, so carbon will done via a different method. The pond filter has a blower on it for backwashing. Is the backwashing the primary maintenance that's needed on these types of filters, or is there something else I should be concerned about?