Heater Bust

So I did a water change today on my ten gallon before I went to work and noticed that there was a crack on my heater afterward. It probably cracked from me not unplugging it like I always used to. I just got lazy and forgot. It was overheating a little, so I figured it just needed to cool down, so I pulled the plug at 4 pm and told my wife to plug it back in when she came home at 7 pm so that it would have a little time to heat up before I got home from work at 11 pm. When I got home I took a look and to my surprise, the heater was completely fried! It had broken in two and had dropped a bunch of nasty black stuff on the water and on the gravel in the tank. Quickly I took out the python and removed as much black stuff as I could and did a big water change. Is there anything else I can do to combat this? Is the stuff inside a heater dangerous to fish? They are going to have to make the night before I can do anything with them. The heater is gone, so room temp will have to do for now until I go back to work tomorrow. Help? Ideas? Similar issues? The fish seem fine and everyone is accounted for and doing well, including the guppy babies, so I doubt this is much of an issue. It is a cheap Wal-Mart heater that is nonadjustable and stays at 78 degrees if that helps. What should I do?

We had this happen with a NEW heater. All we could do was get that black stuff and all the glass (our shattered) out and do a water change. We did a small water change almost every day for a week purely because we didnt know what to do but we didnt have any problems. Hope that helps.