That's a really good idea, too.
They love live plants - if you get live plants, you'll also want to invest in a mini compact flurorescent bulb or two to put in there, and make sure the lights stay on for several hours each day to keep them alive.
The temp of the tank might have a lot to do with the clamped fins. The heater should help. Do you have any little hidey things in your tank, like a rock arch or a cave or anything? They love those too.