Effects of Dried/Dead Coral on Freshwater Tank?

So long as you have completely cleaned the coral by boiling it as you said you have done, it shouldn't have any affect on your water at all. The most would be contribute to an elevated pH, but the size you describe and the size tank you have would probably not be a noticeable elevation. Your convicts are cichlids that are found in central and south America. Being cichlids they would prefer more acidic water with a pH at or just below 7.0. They are easily ed with males having fins that taper into a point at the ends and females being rounded. They can be quite aggressive towards other fish as they are territorial. So keep them with other similar sized or a bit larger fish, preferably other cichlids. They are also very easy to breed. They normally will pair up on their own and begin to build a nest that is a depression in the gravel or in a cave or crevice. When the female begins developing eggs her abdomen will swell and become a bit orange in color. Once the eggs are ready, she will lay them on a flat surface, sometimes like the side of a small cave or a rock. The eggs will stick to this surface. Both parentrs fan the eggs to keep fresh water flowing over them and to keep any debris from aculating around them. The eggs should begin to hatch after just a few days and the babys will be very small. You will be able to see them and they look like a pair of eyes and not much else until they get a few days or weeks older.The parents will defend the babys fearlessly against any other fish that gets too close. It is best to keep only 1 male and several females. That way you avoid more than 1 pair spawning together and thus constantly fighting with one another.