holy bajeebus! if it's blocking the output, what was stopping your filter from overflowing?
that is some serious serious blob gunk!
are you sure it's plant material?
HOLY !@#$ never seen anything like that before. My only advice and practical advice is clean often, very often so no build up. Hows your water params? stock? etc.
This happens quickly, 3-4 weeks, it's blocked completely. I used to clean my HOB every 4-5 weeks just cause, and now when it starts back flushing over the intake, it's like "Whoa, it's been 3 weeks already?"