Some sponges will die with exposure to air. You could try that. Zo's can go quite awhile exposed. Maybe expose it and wait a bit and then toothbrush near it. A pretty sponge can look very nice though. I have some lavender colored ones I wish I had a few more of. Maybe I shouldn't say that though as this time next year I may be cussing them out like I did the mushrooms, and the anthelia before that, and the xenia before that, and the razor caulerpa before that, and so on, and so on,,,,,,