Will, have you tried testing your water for Ammonia? The lethargy of Ace might be due to high levels of ammonia (as fish_doc mentioned) if the tank is not fully cycled (if you don't know what this means, PM me). I'd highly advise that you invest in at least an ammonia test kit, if not ammonia and nitrite test kits. They'll cost you about $8 each. Your ammonia and nitrite readings should be 0 in a well-established tank.
Whether the problem's water quality or illness, it makes good sense to change the water every day or two for a week or two (unless you're dosing with medications, in which case you should follow their instructions). I assume you're just doing the temperature treatment, which I think is adviseable. Just make sure to match the temperature of the water when changing it.