Minimum Tank Size
10-gallon: minimum size for a guppy group. Holds 5-6 adult guppies. Anything smaller forces too much waste concentration.
20-gallon long: ideal entry tank. Holds 10-12 adults plus a few corydoras or shrimp.
29-gallon: holds 15-20 guppies comfortably with bottom-dwellers.
The 1-Inch-Per-Gallon Myth
Forget the old "1 inch of fish per gallon" rule. It ignores fish width, waste output, and territory needs. A better rule for guppies: 1 guppy per 2 gallons in a planted, well-filtered tank.
Heavily planted tanks with strong filtration can push to 1 guppy per 1.5 gallons. Bare-bottom tanks with weak filters should stay at 1 per 3 gallons.
Male-Female Ratio
Always 1 male per 2-3 females. Males chase females constantly to mate. With too few females, individual females get harassed to exhaustion.
All-male tanks work well — males display intensely against each other and you avoid the population explosion of breeding.
- ✦All-female tanks slow breeding but females may still arrive pregnant from the store.
- ✦Endlers can interbreed with guppies — keep separated if you want pure lines.
Population Explosion
A single pregnant female brings 20-50 fry. Within months, those fry breed and the tank can have hundreds of fish. Plan ahead — local fish stores often take guppies as credit, or set up a separate growout tank.