I just finish constuction on my pond and everything. Now I get to decide what to put in it. I got a CK and an RTC that I would like to put in there, but then I would have to put a heater and get some type of covering. It's not a big deal to get all that, but with the winters being pretty cold (top has frozen over before), will a heater really help it keep the pond warm? So which would be a better thing to do...just get Koi or see if a 250w heater can heat a 400g pond to at least 74 degrees during the winter?