Pike Cichlid in my 20 gallon tank?

I have a 20 gallon tank and I want to get a Pike Cichlid. The Chiclid is about 3-4 inches long at this moment, it doesn't look like it has the potential to grow much larger either. It already has most of its color. I was wondering if my tank was large enough to support just this one fish. At the moment I have a Hobby and a Firemouth, which get along well. I am preparing to get rid of them for this Pike Cichlid. I just want to make sure it I am making the right choice.