Fish comparison
Black Molly vs Guppy
How the Black Molly and Guppy compare on care, size, water and temperament, and which fish suits your tank.
By Mike ElmiraUpdated
TL;DR, Black Molly vs Guppy
The Black Molly and the Guppy are close cousins, both in the Poecilia group, so at a glance they ask for a lot of the same things. Both are happy somewhere around 24 to 28 °C and pH 7 to 8, so a single tank can suit either one. Neither is harder than the other to keep, so the choice comes down to look and stocking rather than skill. If tank space is tight, the Guppy needs less room to feel settled; give the Black Molly the nod when you have the litres to spare.
Group compatibility overview
Excellent fit
Every key parameter overlaps and no major conflicts surfaced.
Temperature
- Black Molly24–28 °C
- Guppy22–28 °C
pH
- Black Molly7–8.5
- Guppy6.8–8
Hardness
- Black Molly10–25 dGH
- Guppy8–25 dGH
Full attributes
Every parameter, side by side| Parameter |  FishBlack MollyPoecilia sphenops |  FishGuppyPoecilia reticulata |
|---|---|---|
| Category | Fish | Fish |
| Origin | Central America (selectively bred) | Northeastern South America, naturalised globally |
| Family | Poeciliidae | Poeciliidae |
| Temperature | 24–28 °C | 22–28 °C |
| pH | 7.0–8.5 | 6.8–8.0 |
| Hardness (dGH) | 10–25 | 8–25 |
| Flow rate | Low to Medium | Low to Medium |
| Min tank | 100 L | 45 L |
| Adult size | 8–12 cm | 3–6 cm |
| Difficulty | 1 / 5 | 1 / 5 |
| Lifespan | 3–5 yrs | 1–2 yrs |
| Diet | Omnivore (vegetarian-leaning) | Omnivore |
| Water column | All | Mid to Top |
| Schooling | Loose group | No (live in groups) |
| Plant safe | Yes (mild grazing) | Yes |
| Shrimp safe | Adults only (eats shrimplets) | Yes (with adults; may eat shrimplets) |
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Can you keep Black Molly and Guppy together?
Yes. Their temperature and pH ranges overlap around 24 to 28 °C and pH 7 to 8, so one set of water conditions keeps both comfortable. Match group sizes and cover the usual planted-tank basics and they share a tank fine.
Which is easier to keep, the Black Molly or the Guppy?
They sit at the same care level, both very easy, so neither is the obvious beginner pick. The decision is really about the look you're after.
Do Black Molly and Guppy need the same water?
Close to it. Aim for 24 to 28 °C and pH 7 to 8 and you're in the shared sweet spot for both. Full ranges are in the table above.
What's the main difference between the Black Molly and the Guppy?
Space. The Black Molly wants about 100 litres minimum and the Guppy around 45, so tank size can settle it.