What about lack of oxygen in the tank? Does it appear that any of my guppies are gasping for air? They hang a lot at the top, which I've read they do. As you can see I have great surface agitation from my Fluval 307 (only running at 50%). However, I don't have a lot of open space on my lid. Should I create some more holes in the lid to allow more oxygen between the surface and lid?There are several causes that can cause this condition. But dropsy is a condition itself that shows symptoms.