80 is high, but we've all heard of much higher levels being dealt with so kudos for the catch on that. When fish are suddenly exposed to high nitrate levels, they will usually die within 24 to 48 hours of exposure which leads me to believe yours have been creeping up and not a sudden spike/shock/poisoning which over a long period of time can have an impact but it also sounds as though you may have managed that with perhaps some water changes? The bad part would be to send into nitrate shock by lowering the nitrates very low suddenly and not a stepdown method.
No, the male will remain male unless the female was to pass at which point he would become female if given some alone time in the tank. By adding a smaller clown in that event, the new female would remain just that.
Crypto (Marine ich) is more the common cold in the fish world yet we always dread it. I say that to say this; generally, your initial inquiry of 'dropsy' is not contagious per se but doesn't rule out the chance of other inhabitants with a poor immune system are also lower due to previously mentioned reasons the bacteria would be in the tank.
Your welcome for what I've been attempting to convey. That's why we're here. To discuss issues and help one another.
I'm still hopeful for your clown.
