The Black Molly is also known as the common Black Molly, is a hardy fish that is well suited to beginners. It does well in water between 68 and 82-degrees Fahrenheit and prefers a tank that is larger than 30 gallons. Black Molly’s like when you keep the pH between 7 and 7.8. The Black Molly is a peaceful breed that won’t usually fight with other fish and grows to a length of around 3 inches. These fish are covered in mostly black scales but can have spots of different colors throughout their body.