Mollies
A livebearer that will take brackish water, which few community fish will. It grazes algae off glass and stone most of the day.
Photo by Dnoerholm, CC BY-SA 4.0
Overview
Mollies are livebearers from Mexico through to Colombia, commonly around 3 inches with sailfin varieties reaching 5.5, and they want harder water than most tropical fish. FishBase gives a pH of 7.5 to 8.2 and a hardness range of 11 to 30 dH.
That one line explains most molly problems. A tank set up soft and slightly acidic for tetras is the wrong tank for a molly, and a fish that is chronically stressed by water chemistry is the one that comes down with everything going around.
Temperament
Active, peaceful and always grazing. Mollies work over algae on glass and decor throughout the day and mix well with other calm community fish.
Males pursue females persistently, so two or three females to each male keeps it from becoming constant. Like all livebearers they eat their own young, and a female produces 20 to 150 fry after about 28 days, so a planted tank keeps a few and a bare one keeps almost none.
Care and grooming
Worms, crustaceans, insects and plant matter in the wild, and in a tank they take dried food readily and eat green algae off the glass. Vegetable content matters more for mollies than for most community fish.
Hard, alkaline and warm, from 18 to 28 degrees C, which is 64 to 82 F. They also tolerate brackish water, which is sometimes used as a treatment, though a tank kept permanently brackish limits what else can live in it.
Living and exercise
A 60 cm tank, about 20 gallons, with open swimming water and planting at the sides. Sailfin varieties need more room than the common shortfin kinds because they are half again as long.
Water changes with matched hardness matter here. Topping up a molly tank with soft water slowly moves the chemistry away from what the fish needs, and the effect shows up weeks later as a tank that will not stay healthy for reasons that look unrelated.
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