I am building a 30" x 30" x 18" tank right now, and need to decide if I will use an in-sump or external skimmer. In the past, keeping a tank from getting too hot was a big concern. Using external pumps prevented some heat where the lighting generated a large amount. I will be using LED's for lighting with active cooling on the heat sinks. I also keep my house at 70º-75º F all through the summer, and at 62º-70º F during the winter. What I am wondering is if the heat generated from using an in-sump skimmer would be a good thing, requiring less auxilerary heating? I also wonder if there are any advantages to using an external skimmer other than the heat savings?