Aquariumlivebearer · freshwater
Molly: adult size, tank size & tankmates
The Molly (Poecilia sphenops) grows to about 3.8 in (8 cm SL). It needs a tank at least 35 inches long and about 21 gallons. Keep at least 6 together, at 70–82°F.
How big it really gets
Drawn to scale against common tank lengths. Green bars meet the minimum tank length from our sources.
Needs special care. Needs a 90 cm tank and hard alkaline water; often sold into small soft-water community tanks where it becomes sickly.
Will it fit your tank?
Quick facts
- Adult size
- 3.8 in (8 cm SL)
- Minimum tank
- 35 inches long and about 21 gallons
- Temperature
- 70–82°F
- pH
- 7–8.5
- Hardness
- 15–30 dGH
- Group size
- 6+
- With other fish
- peaceful
- With its own kind
- peaceful
- Swims
- middle of the tank
- Diet
- omnivore
- Care level
- beginner
- Lifespan
- not stated in sources
Watch for: may eat baby shrimp
Molly tankmates
Checked with the same rules as our tank builder: temperature overlap, pH and hardness, predation and mouth size, fin-nipping and temperament. Tank size is left out here; check it in the builder.
Good tankmates
- Celestial Pearl DanioAdult ~1 in · 68–79°F
- Cherry BarbAdult ~2.4 in · 68–81°F
- Rummy-nose TetraAdult ~2.4 in · 73–79°F
- Glowlight TetraAdult ~1.9 in · 75–82°F
- GuppyAdult ~2.8 in · 63–82°F
- PlatyAdult ~2.4 in · 68–79°F
- Endler's LivebearerNeeds careAdult ~1.2 in · 75–86°F
- Honey GouramiAdult ~2.6 in · 72–81°F
- Dwarf GouramiNeeds careAdult ~4.2 in · 72–81°F
- Pearl GouramiAdult ~5.7 in · 75–86°F
Use caution
- Neon TetraMolly (15–30 dGH) and Neon Tetra (1–12 dGH) prefer different water hardness.
- Cardinal TetraMolly (15–30 dGH) and Cardinal Tetra (1–12 dGH) prefer different water hardness.
- Harlequin RasboraMolly (15–30 dGH) and Harlequin Rasbora (1–12 dGH) prefer different water hardness.
- Ember TetraMolly (15–30 dGH) and Ember Tetra (1–10 dGH) prefer different water hardness.
- Chili RasboraMolly (15–30 dGH) and Chili Rasbora (1–10 dGH) prefer different water hardness.
- Black Neon TetraMolly (15–30 dGH) and Black Neon Tetra (1–12 dGH) prefer different water hardness.
- Lemon TetraMolly (15–30 dGH) and Lemon Tetra (1–12 dGH) prefer different water hardness.
- German Blue RamNeeds careMolly and German Blue Ram only share 81–82°F. That's a tight window.
Avoid
- Chinese Algae EaterOutgrows tanksChinese Algae Eater is aggressive toward tankmates. Molly is peaceful.
- Convict CichlidNeeds careConvict Cichlid is aggressive toward tankmates. Molly is peaceful.
- Iridescent SharkOutgrows tanksIridescent Shark eats small fish, and Molly only grows to about 3.8 in.
- OscarOutgrows tanksOscar eats small fish, and Molly only grows to about 3.8 in.
All 105 species we checked against the Molly
| Species | Verdict | Why |
|---|---|---|
| African Dwarf Frog | Compatible | No conflicts found |
| Assassin Snail | Compatible | No conflicts found |
| Bala Shark | Compatible | No conflicts found |
| Betta | Compatible | No conflicts found |
| Black Skirt Tetra | Compatible | No conflicts found |
| Bristlenose Pleco | Compatible | No conflicts found |
| Bronze Cory | Compatible | No conflicts found |
| Buenos Aires Tetra | Compatible | No conflicts found |
| Bumblebee Goby | Compatible | No conflicts found |
| Celestial Pearl Danio | Compatible | No conflicts found |
| Cherry Barb | Compatible | No conflicts found |
| Clown Pleco | Compatible | No conflicts found |
| Common / Comet Goldfish | Compatible | No conflicts found |
| Common Pleco | Compatible | No conflicts found |
| Congo Tetra | Compatible | No conflicts found |
| Denison Barb | Compatible | No conflicts found |
| Dwarf Gourami | Compatible | No conflicts found |
| Dwarf Neon Rainbowfish | Compatible | No conflicts found |
| Electric Yellow Lab | Compatible | No conflicts found |
| Endler's Livebearer | Compatible | No conflicts found |
| Forktail Blue-eye | Compatible | No conflicts found |
| Giant Danio | Compatible | No conflicts found |
| Glowlight Tetra | Compatible | No conflicts found |
| Gold Barb | Compatible | No conflicts found |
| Guppy | Compatible | No conflicts found |
| Head-and-tail-light Tetra | Compatible | No conflicts found |
| Honey Gourami | Compatible | No conflicts found |
| Japanese Trapdoor Snail | Compatible | No conflicts found |
| Malaysian Trumpet Snail | Compatible | No conflicts found |
| Moonlight Gourami | Compatible | No conflicts found |
| Odessa Barb | Compatible | No conflicts found |
| Paradise Fish | Compatible | No conflicts found |
| Pea Puffer | Compatible | No conflicts found |
| Pearl Danio | Compatible | No conflicts found |
| Pearl Gourami | Compatible | No conflicts found |
| Penguin Tetra | Compatible | No conflicts found |
| Platy | Compatible | No conflicts found |
| Pristella Tetra | Compatible | No conflicts found |
| Ramshorn Snail | Compatible | No conflicts found |
| Rosy Barb | Compatible | No conflicts found |
| Rummy-nose Tetra | Compatible | No conflicts found |
| Serpae Tetra | Compatible | No conflicts found |
| Siamese Algae Eater | Compatible | No conflicts found |
| Silver Tip Tetra | Compatible | No conflicts found |
| Sterbai Cory | Compatible | No conflicts found |
| Swordtail | Compatible | No conflicts found |
| Tiger Barb | Compatible | No conflicts found |
| Upside-down Catfish | Compatible | No conflicts found |
| Variatus Platy | Compatible | No conflicts found |
| White Cloud Mountain Minnow | Compatible | No conflicts found |
| Zebra Danio | Compatible | No conflicts found |
| Amano Shrimp | Caution | Molly may eat baby Amano Shrimp. Adults are usually safe, but expect fewer shrimplets. |
| Angelfish | Caution | Angelfish can bully smaller, peaceful Molly. |
| Bamboo Shrimp | Caution | Molly may eat baby Bamboo Shrimp. Adults are usually safe, but expect fewer shrimplets.; Molly (15–30 dGH) and Bamboo Shrimp (6–10 dGH) prefer different water hardness. |
| Black Neon Tetra | Caution | Molly (15–30 dGH) and Black Neon Tetra (1–12 dGH) prefer different water hardness. |
| Bleeding Heart Tetra | Caution | Molly (15–30 dGH) and Bleeding Heart Tetra (1–12 dGH) prefer different water hardness. |
| Blood Parrot Cichlid | Caution | Blood Parrot Cichlid can bully smaller, peaceful Molly. |
| Boesemani Rainbowfish | Caution | Molly and Boesemani Rainbowfish only share 81–82°F. That's a tight window. |
| Bolivian Ram | Caution | Molly (15–30 dGH) and Bolivian Ram (1–10 dGH) prefer different water hardness. |
| Cardinal Tetra | Caution | Molly (15–30 dGH) and Cardinal Tetra (1–12 dGH) prefer different water hardness. |
| Cherry Shrimp | Caution | Molly may eat baby Cherry Shrimp. Adults are usually safe, but expect fewer shrimplets.; Molly (15–30 dGH) and Cherry Shrimp (6–14 dGH) prefer different water hardness. |
| Chili Rasbora | Caution | Molly (15–30 dGH) and Chili Rasbora (1–10 dGH) prefer different water hardness. |
| Clown Killifish | Caution | Molly (15–30 dGH) and Clown Killifish (1–8 dGH) prefer different water hardness. |
| Clown Loach | Caution | Molly (15–30 dGH) and Clown Loach (1–12 dGH) prefer different water hardness. |
| Cockatoo Dwarf Cichlid | Caution | Molly (pH 7–8.5) and Cockatoo Dwarf Cichlid (pH 5–6) prefer different pH. |
| Crystal Red Shrimp | Caution | Molly may eat baby Crystal Red Shrimp. Adults are usually safe, but expect fewer shrimplets.; Molly (15–30 dGH) and Crystal Red Shrimp (4–6 dGH) prefer different water hardness. |
| Diamond Tetra | Caution | Molly (15–30 dGH) and Diamond Tetra (5–12 dGH) prefer different water hardness. |
| Discus | Caution | Molly (15–30 dGH) and Discus (0–5 dGH) prefer different water hardness. |
| Electric Blue Acara | Caution | Electric Blue Acara can bully smaller, peaceful Molly. |
| Ember Tetra | Caution | Molly (15–30 dGH) and Ember Tetra (1–10 dGH) prefer different water hardness. |
| Fancy Goldfish | Caution | Molly and Fancy Goldfish only share 70–70°F. That's a tight window. |
| Firemouth Cichlid | Caution | Firemouth Cichlid can bully smaller, peaceful Molly. |
| German Blue Ram | Caution | Molly and German Blue Ram only share 81–82°F. That's a tight window.; Molly (15–30 dGH) and German Blue Ram (1–10 dGH) prefer different water hardness. |
| Ghost Shrimp | Caution | Molly may eat baby Ghost Shrimp. Adults are usually safe, but expect fewer shrimplets. |
| Glass Catfish | Caution | Molly (15–30 dGH) and Glass Catfish (1–10 dGH) prefer different water hardness. |
| Harlequin Rasbora | Caution | Molly (15–30 dGH) and Harlequin Rasbora (1–12 dGH) prefer different water hardness. |
| Hillstream Loach | Caution | Molly (15–30 dGH) and Hillstream Loach (1–10 dGH) prefer different water hardness. |
| Julii Cory | Caution | Molly (15–30 dGH) and Julii Cory (1–12 dGH) prefer different water hardness. |
| Kissing Gourami | Caution | Kissing Gourami can bully smaller, peaceful Molly. |
| Kribensis | Caution | Molly (15–30 dGH) and Kribensis (0–12 dGH) prefer different water hardness. |
| Kuhli Loach | Caution | Molly (15–30 dGH) and Kuhli Loach (0–8 dGH) prefer different water hardness. |
| Lambchop Rasbora | Caution | Molly (15–30 dGH) and Lambchop Rasbora (1–10 dGH) prefer different water hardness. |
| Lemon Tetra | Caution | Molly (15–30 dGH) and Lemon Tetra (1–12 dGH) prefer different water hardness. |
| Marbled Hatchetfish | Caution | Molly (15–30 dGH) and Marbled Hatchetfish (1–10 dGH) prefer different water hardness. |
| Mystery Snail | Caution | Molly (pH 7–8.5) and Mystery Snail (pH unknown) prefer different pH.; Molly (15–30 dGH) and Mystery Snail (unknown dGH) prefer different water hardness. |
| Neon Tetra | Caution | Molly (15–30 dGH) and Neon Tetra (1–12 dGH) prefer different water hardness. |
| Nerite Snail | Caution | Molly (15–30 dGH) and Nerite Snail (6–12 dGH) prefer different water hardness. |
| Otocinclus | Caution | Molly (15–30 dGH) and Otocinclus (1–12 dGH) prefer different water hardness. |
| Panda Cory | Caution | Molly (15–30 dGH) and Panda Cory (1–12 dGH) prefer different water hardness. |
| Peppered Cory | Caution | Molly (15–30 dGH) and Peppered Cory (0–12 dGH) prefer different water hardness. |
| Pictus Catfish | Caution | Pictus Catfish can bully smaller, peaceful Molly.; Molly (pH 7–8.5) and Pictus Catfish (pH 5.8–6.8) prefer different pH. |
| Pygmy Cory | Caution | Molly (15–30 dGH) and Pygmy Cory (0–8 dGH) prefer different water hardness. |
| Rainbow Shark | Caution | Rainbow Shark can bully smaller, peaceful Molly. |
| Red-Tail Shark | Caution | Red-Tail Shark can bully smaller, peaceful Molly. |
| Scissortail Rasbora | Caution | Molly (15–30 dGH) and Scissortail Rasbora (2–12 dGH) prefer different water hardness. |
| Silver Hatchetfish | Caution | Molly (15–30 dGH) and Silver Hatchetfish (1–12 dGH) prefer different water hardness. |
| Sparkling Gourami | Caution | Molly (15–30 dGH) and Sparkling Gourami (1–12 dGH) prefer different water hardness. |
| Three-spot Gourami | Caution | Three-spot Gourami can bully smaller, peaceful Molly. |
| Tinfoil Barb | Caution | Molly (15–30 dGH) and Tinfoil Barb (2–10 dGH) prefer different water hardness. |
| Weather Loach | Caution | Molly (15–30 dGH) and Weather Loach (1–12 dGH) prefer different water hardness. |
| Yoyo Loach | Caution | Yoyo Loach can bully smaller, peaceful Molly.; Molly (15–30 dGH) and Yoyo Loach (2–12 dGH) prefer different water hardness. |
| Chinese Algae Eater | Avoid | Chinese Algae Eater is aggressive toward tankmates. Molly is peaceful. |
| Convict Cichlid | Avoid | Convict Cichlid is aggressive toward tankmates. Molly is peaceful. |
| Iridescent Shark | Avoid | Iridescent Shark eats small fish, and Molly only grows to about 3.8 in. |
| Oscar | Avoid | Oscar eats small fish, and Molly only grows to about 3.8 in. |
Care notes
Needs: Hard, alkaline water is essential; much more disease-prone in soft or acidic water. Added salt is optional (SF says hard minerals matter more) but morphs do better in slightly brackish water. Needs plenty of vegetable food. Only house with fish that tolerate the same hard water.
Group: SF does not rate social needs (unknown) but advises several females per male because males pursue females relentlessly; 6 editorial. All-female groups avoid harassment.
Temperament: peaceful toward other fish, peaceful toward its own kind. Lives in the middle of the tank.
Common questions
How big does a Molly get?
About 3.8 inches (8 cm SL) as an adult, according to seriouslyfish.com.
What size tank does a Molly need?
At least 35 inches long and about 21 gallons. The smallest standard tank that meets that is a 40 gallon breeder.
How many Mollys should be kept together?
At least 6. SF does not rate social needs (unknown) but advises several females per male because males pursue females relentlessly; 6 editorial. All-female groups avoid harassment.
What fish can live with a Molly?
Species that passed every check include Celestial Pearl Danio, Cherry Barb, Rummy-nose Tetra, Glowlight Tetra, Guppy, Platy.
Gear for a Molly setup
TankSmallest standard tank that meets its minimum: 40 gallon breeder (36 in long).Find on Amazon →HeaterAbout 200 W for 40 gallons, holding 70–82°F.Find on Amazon →FoodA quality flake or micro-pellet as a staple.Find on Amazon →Test kitCheck ammonia, nitrite and pH. Cycle the tank before adding fish.Find on Amazon →
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Related guides
Sources
Values come from these pages, in our own words. Status: verified (independent spot-check). Last reviewed 2026-10-12.
- seriouslyfish.com /species/poecilia-sphenops/
- fishbase.se /summary/Poecilia-sphenops.html
- fishbase.se /summary/Poecilia-latipinna.html