Can i keep a 2 inch malawi cichlid in a 20 gallon terrarium?

Ok i have my 2 inch Malawi Cynotilapia Cichlid in a 10 gallon tank all alone :( and i have an empty 20 gallon terrarium, i have a 30 gallon aquarium right next to it and the thickness of the gl is exactly the same and the sealant on the corners looks and feels the same as in my 30 gallon and other aquariums. can i use it as an aquarium? also if i can how many other Malawi Cichlids can i have in the tank with it? (Im going to have alot of rock caves and hiding places)