Black Molly Fish Care - It is recommended that Mollies be placed in aquariums containing at least 15 gallons of water, a maximum of ¼ inch of gravel, and a heater that keeps the temperature of the water between 78 and 82 degrees Fahrenheit. As with Guppies and other livebearers, you should put 1 tablespoon of aquarium salt per 5 gallons of water to help them survive better in fresh water environments. Unique to the Mollies species of fish, they can actually live quite well in complete salt water aquariums as well. Since Mollies have this flexibility, they are a versatile fish that could be compatible in many different aquarium set ups |