Guppy vs Molly
Two hardy, hard-water livebearers for a peaceful community. The guppy is small, colourful and space-efficient; the molly is a bigger, bolder grazer that needs more room. Here's which fits your tank.
The quick verdict
Both love the same hard, alkaline water and both breed freely, so the deciding factor is size and space. Choose the guppy for a smaller tank, vivid fancy tails and an easy first fish. Choose the molly if you have 75 litres or more and want a larger, characterful algae-grazer. They also make excellent tankmates for each other.
| Guppy | Molly | |
|---|---|---|
| Care level | Beginner | Beginner |
| Min tank size | 40 L / 10 gal | 75 L / 20 gal |
| Temperament | Peaceful | Peaceful |
| Adult size | 3–6 cm | 6–10 cm (bulky) |
| Water | Hard, pH 7.0–8.0 | Very hard, pH 7.5–8.5 |
| Best for | Smaller tanks, colour | Bigger tanks, algae grazing |
The real differences
It's mostly about bulk and bioload. Guppies are small and space-efficient, so a group settles into 40 litres. Mollies reach 6–10 cm, are surprisingly heavy-bodied and produce a lot of waste, so they need at least 75 litres and strong filtration. Mollies also lean more herbivorous, grazing algae and appreciating spirulina-based foods, and they want even harder, more mineral-rich water than guppies. Both are prolific livebearers, so plan for fry with either.
Which should you buy?
Our pick
For a small-to-medium first tank, the guppy is the more flexible, forgiving pick. If you have the space and filtration for a bigger, bolder fish that helps graze algae, the molly is full of character. Read the guppy care guide and molly care guide, or size up your options in our aquariums guide.
Frequently asked questions
Are guppies or mollies easier to keep?
Guppies are a little more forgiving because they are small and need less space — a group is fine in 40 litres. Mollies are just as hardy but larger (6–10 cm), messier, and want at least 75 litres with strong filtration. Both are beginner livebearers that thrive in hard, alkaline water.
Can guppies and mollies live together?
Yes. They are both peaceful livebearers that love the same hard, alkaline water, so they make natural tankmates in a tank of 75 litres or more. Just remember mollies are much bigger and heavier waste producers, so size the tank and filter for them.
Do mollies need salt and guppies don't?
Neither strictly needs salt. Mollies do best in very hard, mineral-rich water and can tolerate brackish conditions, but pure fresh water is fine as long as it is hard. Guppies are equally happy in hard tap water without any salt.
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