Molly (Common / Sailfin) Tank Mates

Mollies are big, active, peaceful livebearers that suit a roomy community with hard, slightly alkaline water.

They get along with most peaceful fish but are larger and messier than guppies, so they need more space and stronger filtration. The engine clears the usual community crowd; plan for breeding and for their preference for harder water (some keepers add a little salt, which limits invertebrate tankmates).

Molly (Common / Sailfin) key facts

The sourced figures the engine uses to judge Molly (Common / Sailfin) pairings.

Top Molly (Common / Sailfin) tank mates

A ranked shortlist: the species the engine clears with Molly (Common / Sailfin) and that suit its size and temperament best — tap a name for its care guide, or use + Add to test the pairing in the planner.

No tank mates match these filters — try removing one. Reset filters

Other engine-cleared options (not necessarily ideal)

These clear TankStocking's hard welfare checks with Molly (Common / Sailfin), but are larger, bolder, or otherwise less ideal than the shortlist above — read up before committing.

Possible with care

These can work, but the engine flags something to watch — read the reason before you commit.

• Betta (Siamese Fighting Fish) — Territorial
• Paradise Fish — Aggression
• Five-banded Barb — Heavily stocked
• Gold Barb — Heavily stocked
• Odessa Barb — Heavily stocked
• Tiger Barb — Heavily stocked
• Cockatoo Dwarf Cichlid (Apisto Cacatuoides) — Territorial
• Convict Cichlid — Aggression
• Firemouth Cichlid — Territorial
• Jewel Cichlid — Aggression
• Kribensis (Rainbow Krib) — Territorial
• Oscar — Aggression
• Bronze Corydoras — Heavily stocked
• Sterbai Corydoras — Heavily stocked
• Pearl Danio — Heavily stocked
• Golden Wonder Killifish (Striped Panchax) — Aggression

Best avoided

A hard welfare check fires for each of these — don't mix them with Molly (Common / Sailfin).

• Chocolate Gourami — Species-only fish
• Licorice Gourami — Species-only fish
• Rosy Barb — Temperature clash
• Tinfoil Barb — Predation risk
• Discus — Temperature clash
• Green Severum — Predation risk
• Multifasciatus Shell-Dweller — Territorial, Species-only fish
• Common Goldfish — Temperature clash, Coldwater + tropical
• Fancy Goldfish — Temperature clash, Coldwater + tropical
• Gold White Cloud Mountain Minnow — Temperature clash, Coldwater + tropical
• Rosy Red Minnow (Fathead Minnow) — Temperature clash, Coldwater + tropical, Heavily stocked
• White Cloud Mountain Minnow — Temperature clash, Coldwater + tropical
• Peppered Corydoras — Temperature clash, Heavily stocked
• Dwarf Emerald Rasbora — Temperature clash

Keeping Molly (Common / Sailfin) well: the detail

Beyond the table — the behaviour, the parameters that actually move the needle, and the mistakes that cost fish. Hobbyist context, not a verdict; the planner above is what judges your plan.

Water parameters in practice

Mollies are the hardest-water fish on this list: they need genuinely hard, alkaline water (GH 15–30 dGH, pH 7.5–8.5) and visibly struggle in soft, acidic tanks. Do not soften the water for them — if anything, harder is better. They are large and messy, so strong filtration and a roomy tank are part of the parameter set, not extras.

Why Molly (Common / Sailfin) behaves the way it does

Mollies come from hard, mineral-rich coastal and brackish waters of Central America, where some populations live in genuinely salty estuaries. That ancestry is why they crave hardness, tolerate a little salt, and carry a heavier build and bio-load than a guppy or platy. They are active, social grazers that browse algae and biofilm all day.

Common Molly (Common / Sailfin) stocking mistakes

The first mistake is keeping mollies in soft water, which quietly stresses them and invites disease. The second is underestimating their size and waste — common mollies want 20 gallons and sailfins 30-plus, with filtration to match. The third is reflexively adding salt: mollies do not need it in freshwater, and it rules out shrimp and many catfish.

Early signs something is wrong

The molly tell-tale is "the shimmies" — a fish that shudders and swims on the spot without going anywhere, almost always a sign of soft water, cold, or poor quality. Clamped fins, gasping at the surface, and white patches follow from the same neglect. A thriving molly grazes constantly and holds its dorsal high.

How tank size changes the answer

Common mollies need at least 20 gallons; sailfins, which reach a hefty 12–15 cm, want 30 or more for their size and their waste. The extra volume is about bio-load as much as swimming room — crowd mollies and water quality collapses fast. A mixed group breeds readily, so plan for fry or keep one sex.

Molly (Common / Sailfin) community ideas

Each build is scored by the same engine as the planner — tap one to load it.

Common questions

More on Molly (Common / Sailfin)

Related guides on TankStocking — each scored by the same welfare engine as the planner.

Compatibility is a planning estimate: individual temperament, tank layout, and group sizes all matter. Cycle the tank, add fish gradually, and watch how they behave. See the methodology or browse the full freshwater fish list.