Aquarium Setup: The aquarium architecture MUST accommodate their large size, immense swimming energy, and massive waste production. A minimum 100-liter (25-gallon) LONG tank is absolutely mandatory; cramped tanks cause severe stress and aggression. The tank should feature open swimming space, very bright lighting to cultivate green algae (which they eat constantly), and hardy plants (like Anubias or Vallisneria). A crushed coral or aragonite sand substrate is highly recommended to naturally buffer the pH and hardness.
Diet and Feeding: They are highly active omnivores with a massive, absolute biological requirement for vegetable matter. In the aquarium, they are phenomenal algae eaters, constantly grazing on green fuzz algae. However, their diet MUST be heavily supplemented. They strictly MUST be fed a premium, plant-heavy diet. Daily offerings of high-quality spirulina flakes, algae wafers, and blanched vegetables (zucchini, spinach) are unconditionally mandatory for their digestion, supplemented only occasionally with meaty foods (bloodworms).
Water Quality: This is the single most critical aspect of their care: Mollies are EXTREME HARD WATER fish. They strictly demand extremely hard, alkaline water (GH 15-30, pH 7.5 - 8.5) and warm tropical heat (25-28°C / 77-82°F). Keeping them in soft, acidic water (below pH 7.0) is a death sentence; their immune system will instantly collapse, resulting in "the shimmies" (a fatal neurological rocking motion). The addition of marine salt (1 tablespoon per 5 gallons) is highly beneficial and often necessary for optimal health.
Compatibility and Cohabitation: Compatibility is generally good, provided water chemistry requirements are met. They are large, active, and occasionally bossy. They MUST NEVER be housed with soft-water fish (like Discus, Tetras, or Rams) as their water requirements are exact opposites. They MUST NEVER be housed with aggressive fin-nippers. Excellent companions include other large, hard-water livebearers (Swordtails, Platies) and certain hard-water Rainbowfish. They are also excellent candidates for true brackish water setups with Gobies or Puffers.
Aquarium Breeding: Breeding Mollies is explosive and effortless. They are livebearers, giving birth to massive, fully formed fry. A single mating allows the female to produce massive broods (up to 100+ fry) every 30 days for months. Because they are large fish, the fry are born exceptionally large and can eat crushed flakes immediately. Adult Mollies are voracious cannibals and will aggressively hunt their own fry. Massive thickets of dense plants (like Guppy Grass) or a separate rearing tank are mandatory for fry survival.
Risks and Diseases: The absolute greatest physical risk is severe immune collapse, "the shimmies," and death caused by keeping them in soft, acidic water; extremely hard, alkaline water (often with salt) is unconditionally mandatory. The second major risk is lethal stress for females kept in improper ratios; failing to provide 2-3 females per male guarantees the females will be harassed to death. Finally, their massive appetite means they produce immense waste; poor filtration guarantees lethal bacterial spikes.