It may be a stupid question, but here ya go. I've got 8 Buff Orpington chicks. Almost 3 weeks old. I was using a large plastic bin in the spare room bathtub as a brooder. They've since out grown that and I just have them in the tub with a wooden frame on top covered with hardware cloth. So I started them out at 90 degrees and have been dropping the temp by 5 degrees every week. My question is, since they are inside in a stable temperature environment (72 degrees), at what point do I take the heat lamp away completely?