Hello all. I wear Oceanic Vortex 12 splits with my drysuit. They have a matte type finish and they have gotten quite...skanky. I soaked them in a dive gear enzyme cleaner but they are still just cruddy...with saltwater/seascummy gooey yuck still encrusted on them. My Apollos Bio-fins are also black but never look gross, I just rinse them out and they are fine. Any tried and proven cleaning tips??? I've scrubbed them with a regular brush and the crud is resistant to that...I used an iron bristle (a fine one...not too rough) and it seems to work but I'm worried it might damage the rubber. Any tips appreciated!!! Thanks.