Difficulty:Beginner Max Growth Size:6 cm Temperament:Peaceful, community Water Parameters:Temperature:20-26 degrees celsiuspH Level:7.0-8.0General Hardness:Moderate Mollies are one of the most popular aquarium fish species because they are pretty easy to keep and not too demanding. Unfortunately, though, many mollies die a premature death from being kept in unsuitable setups. Tank size. Some sources recommend these fish for aquariums as small as 5 gallons (19L) but they actually need a much more spacious tank. To keep your mollies happy and healthy provide them with an aquarium of at least 35″ (90cm). Don’t keep them alone or in pairs: a harem consisting of one male and two females is the minimum number for these fish. More is always better, though, as they love plenty of company. Water quality. Your molly tank should always be filtered, heated and fully cycled. Like most livebearers but unlike many other popular aquarium fish species mollies don’t appreciate soft, acidic water. Hard water with a pH of at least 7 is needed to keep them healthy. Salt. Another interesting and highly debated point is salt. Most aquarists keep mollies in freshwater setups and have no idea their fish can actually thrive in brackish or even marine water. While fresh water should be fine as long as water quality is high many molly keepers swear their fish seem healthier with a bit of added salt.