First:

Is it just a fluke that I don't need a heater in my 55 gallon tank? All summer long, my temp stays around 80-82 degrees. In the winter (like this time of year) it's at 78-80 degrees. I don't have a heater. I guess I should probably get one just in case the power goes out. But, even then, the fish and corals would die from lack of oxygen rather than the cold. Is it just that the tank is small enough or what?

Second:

What's the deal with calcium? I don't keep sps corals, so I guess Ca is not a big concern of mine. Should it be, though? I have some soft corals, but that's it. Is dosing with Kalkwasser (sp?) just a way to increase or maintain the calcium level? Same for the Ca reactors? And, just what is Kalk anyway?

I see this stuff all the time in these forums. Just thought someone could fill me in.