Hi everyone I'm new here. I got a 10 gallon tank recently and have it overstocked. I have 3 golden molleys 2 rainbow sharks 3 zebra catfish and 2 Plecos. I am about to buy a 30 gallon tank on Craigslist. I know this isn't big enough either but it will help for now until I return to work and can buy a bigger tank. But my question is that the 30 gallon tank this person is selling has a jack Dempsey in it and they seem like they are going to just throw away the fish if I don't take it with the tank. Will this jack Dempsey just kill everything that I have in my ten gallon that I plan on putting in the 30 gallon?