Ok well at the least, you need to take it to the sink and toothbrush all the surfaces and strings so you can see the white again. The slime is not allowing more gha to attach. And there might be food particles rotting on the bottom of the box.
After that, run the light for 22 hours a day, and of course bubbles for 24 hours a day. Also check the air tube outlets for lime buildup (clean with a paper clip). The FW will also remove any pods.
If you remove gfo now the scrubber might grow dark, so wait on that.
Taking it to the sink is more work, it does make for better filtering.