"you might die from a fungal infection from whatever fungus grows in BCD's."
We were taught to unscrew the inflator hose and RINSE the inside of the BC after every dive, because otherwise salt crystals can and will build up, and those are abrasive enough to eventually cut through the bladder.
Dude, you know you can make some water come in using the inflator, right? Press the deflate button, let a bit of water go in, move it around a bit, empty it and be done with that. Takes 1 minute tops.
And yes, you can get **** to grow in BCDs. Some even found small mussels in their BC . Unsurprisingly, they found it after I and a few others explained to them why we were not gonna "breathe the air out of the BCD in order to descend fast". Needless to say, they don't breathe in those things anymore.
Also, since there's absolutely no need for chemicals, why not just like... not use them? Even if you use them, your bc is not gonna be "breathable air" anyway, this is completely pointless to do and simply a waste of time, money and against the environment .