Tank Crash - Fish Breathing Heavy..

[ScubaSteve]

When you stir up the tank such as you have you can release a lot of trapped organics and nitrates, all of which will fuel a bacterial bloom which consumes oxygen. I think this might be your problem. Surface agitation doesn't mean much of you aren't getting o2-rich water down to the bottom. Get a powerhead down low and aim it up. Get an airstone in there to help aerate the water until your have a skimmer up.