New to chick raising here, but not new to animals. In places where disease spreads quickly, I would say clean often, but in my home where the environment is controlled and there's no diseases to be found, I'm not going to clean my brooder too often, unless it stinks. I've got 15 chicks in a a refrigerator box, with water elevated. We live in a dry environment (10,000 feet in the rockies) so mold won't be a problem. They seem a bit crowded, but that's what they'll have to live with until it stops snowing (end of May), or they're big enough to stay warm in the greenhouse. I have to agree with the idea that they're not going to live a "clean" life outside, so unless there is disease present, let em be dirty. They are dirty little birds after all. Eating each other's poop, dusty, worm eating, goofy looking creatures, but boy do they make life delicious!