Sponges can’t be exposed to air. Do you have a pic? I’m guessing it can’t be a sponge. And it shouldn’t be hard.I've added half a cap of Prime, and did a 10% water change with live water with added synthetic salt to bring salinity from 1.018 to 1.030 in the source, and 1.024 in the tank. I removed any detritus and brown algae from the sand, and I'm quite sure I wiped out a baby colony of sponge in the process. The sponge came free with the ocean sand and I'm not even confident that it is a sponge because it has never become solid. The one torch which was bleeching has been gone for 2 days, I suspect its gone forever. It has about 1 to 2 mm of tentacles showing but I've seen that happen on another torch that only had about 5 tentacles remaining and it died within days. The remaining 4 torches, star coral, and clownfish, seem to be thriving. If they last a few more weeks I'll upgrade to LED.