Hi everyone, yesterday,one of my leopard Danios,was looking very poor.Floating on his side, laying on the bottom of the tank.This morning,he was lying vertical in a plant,I thought he'd gone.I got my net,to retrieve him,but to my amazement,he swam off. He was listing badly,all over the place.I am going to test the water now,though, in my panic yesterday,I did a 50% water change.Is there any hope for him,should I put him out of his misery? Thanks