Dave, if your babies are caking and clogging up on the outside, they are probably also clogging inside the intestines, too. That's what's killing the chicks. I recommend you give solid coconut oil, about a teaspoon, to each chick that comes up with pasty butt, and smooth a bit of the oil on the vent after you clean them off.
The cause of pasty butt can be several things. One is they aren't drinking enough water. Another is that the brooder is too small to permit the chicks from accessing cool spaces in which to shed excess body heat. In tropical climes, it's going to be a challenge to provide cooling off space, but you might consider using a very low-wattage bulb as a heat source instead of one that is capable of cooking meat.
The cause of pasty butt can be several things. One is they aren't drinking enough water. Another is that the brooder is too small to permit the chicks from accessing cool spaces in which to shed excess body heat. In tropical climes, it's going to be a challenge to provide cooling off space, but you might consider using a very low-wattage bulb as a heat source instead of one that is capable of cooking meat.