[Murk]

^That's a good one.

I'm not sure why the slime would come so aggressively. I can only think of three reasons:

When you clean the filter (which you now do every week) - how do you do it? If you do a real "deep clean" every week (chlorine, boiling water, really scrubbing hard, etc.) that will probably mess up any bacteria population in there.

Is there any "active" material in the cannisters - chemical filtration or even just activated carbon? Those do wear out after some time and might need to be replaced.

Could there be a slime colony somewhere else in the aquarium, somewhere in a dirty corner or under some rocks? That would at least explain where the new slime comes from after each clean.