Mollies are good starting fish, they are also accustomed to saltwater, thats actually when they thrive the most. I have a freshwater 29 gallon in which I have Mollies in and they have lasted me over 2 1/2 years and they just keep reproducing, its unbelievable!! The secret is adding some salt to your freshwater tank. But if you like the green Chromis I would go for them, thats what I used in my 180 Reef and I've had them for about a year, their a great looking fish and they school together, I have 6.