I have the 280...You COULD use ceramic rings or the like...I just use
a square spong filter from a xp3 jammed in there and rinse it in tank water
every few days. Pretty easy to clean that way..rather than rinsing out the rings...also I took out the sponge and vacuumed out the bottom of the filter
when I did a wc today. (I also use a #4 in tank sponge filter)
As far as I understand the guru's use no carbon or zeolite...pretty much
sponges that can be rinsed in the water from a waterchange...not the tap.
Am I close?