Best fish for a 5 gallon tank (and how many)

Best fish for a 5 gallon tank

In order of how well they suit a 5 gallon tank. "Up to" is the most of that one species the tank holds on its own; mixing species splits it.

1. 1.Betta Betta splendens

   2.5" adult · one is fine · 76–82 °F · pH 6.5–7.5 · up to 1 in a 5 gallon

   The classic 5 gallon fish, kept on its own: Seriously Fish says bettas are best kept alone and aren't suited to a community tank.^[4] In a 2024 welfare study, bettas in the largest tank tested (19.3 L, about 5 gallons) were more active and showed fewer abnormal behaviours than those in smaller tanks.^[5] It needs a heater; our species data puts it at 76–82 °F.

2. 2.Least killifish Heterandria formosa

   1.2" adult · groups of 3+ · 68–78 °F · pH 7–8 · up to 4 in a 5 gallon

   One of the very few fish that genuinely suit 5 gallons. Despite the name it's a livebearer, and Seriously Fish says a pair fits a 12.5 L (about 3.3 gallon) tank and a small colony is best.^[6] Keep it on its own: the males are under an inch and most other fish will eat them.^[6]

Shrimp and snails for a 5 gallon tank

Listed separately: the fish bio-load budget below doesn't describe invertebrates, so they aren't counted in it.

• Cherry shrimp Neocaridina davidi

  Aquarium Co-Op says cherry shrimp can live in a nano as small as 2 gallons, with 10 or more better for a colony; buy at least 10 to get both sexes.^[7]

• Nerite snail Neritidae (e.g. Vittina natalensis)

  An algae grazer that Aquarium Co-Op says can live in a tank as small as 2–3 gallons.^[8]

• Dwarf orange crayfish Cambarellus patzcuarensis

  Amazonas magazine says a pair of dwarf orange crayfish can easily live in a 5 gallon tank.^[9]

How many of each fish fit in a 5 gallon tank

A 5 gallon (16 × 8 × 10 in) holds about 4 gallons of water once you take off the glass. Our stocking calculator budgets that water by adult size and body shape: about 0.8 gallons per inch of slim fish (tetras, rasboras), 1.2 for medium-bodied fish (guppies, corys) and 2 for heavy, messy fish (goldfish, plecos). That works out to roughly 5 inches of small, slim adult fish in total. It is an upper limit, not a target: filtration, plants, territory and how often you change water all move it.

Stocking ideas for a 5 gallon tank

Stocking plans that fit the tank's bio-load budget, with a temperature and pH range that suits everything in them.

Fish to avoid in a 5 gallon tank

• Guppy · needs 10+ gallons

  Seriously Fish's smallest footprint for guppies is 45 × 30 cm (about 18 × 12 inches).^[2]

• Neon tetra · needs 15+ gallons

  Neons need a group of 8–10 and a 60 × 30 cm (24 × 12 inch) footprint, per Seriously Fish.^[1]

• Endler's livebearer · needs 10+ gallons

  Often sold for nano tanks, but Seriously Fish's footprint for a group is 45 × 30 cm, and they breed prolifically.^[3]

• Dwarf gourami · needs 15+ gallons, 24 in long

  Needs 15 gallons or more for one male, and Seriously Fish reports that dwarf gourami iridovirus, which is untreatable, is widespread in farmed stock.^[10]

• Fancy goldfish · needs 40+ gallons, 36 in long

  Grows to around 8 inches and produces heavy waste; our species data starts fancy goldfish at 40 gallons.

5 gallon tank FAQ

How many fish can go in a 5 gallon tank?

One betta, or a colony of three or four least killifish. A 5 gallon holds about 4 gallons of water, which our bio-load method budgets at roughly 5 inches of small, slim fish, and most schooling fish also need a bigger footprint than 16 × 8 inches.^{[1, 3]} Shrimp and snails are listed separately because the fish budget doesn't describe them.

Can a betta live in a 5 gallon tank?

Yes. Five gallons (about 19 L) matches the best-performing tank in a 2024 welfare study, where bettas were more active and showed fewer abnormal behaviours than in 1.5–5.6 L tanks.^[5] RSPCA Australia calls 10 L the absolute minimum and 20 L or more ideal.^[11] Seriously Fish suggests a 45 × 30 cm footprint, closer to a 10 gallon, so bigger is better.^[4]

Can I put other fish with a betta in a 5 gallon tank?

No. Seriously Fish says bettas are best kept alone and aren't suited to a standard community tank,^[4] and by bio-load a 5 gallon has room for one betta and nothing else. A nerite snail is the usual companion.

Can fish live in a 2.5 gallon tank?

Not well. RSPCA Australia's absolute minimum for a betta is 10 L, a little more than a 2.5 gallon (9.5 L),^[11] and the smallest footprint in the fish profiles we checked, for a pair of least killifish, is 12.5 L.^[6] Cherry shrimp and nerite snails are the realistic options.^{[7, 8]}

How many guppies can you put in a 5 gallon tank?

None, by Seriously Fish's standard: guppies need about an 18 × 12 inch footprint, which a 5 gallon (16 × 8 inches) doesn't have.^[2] A 10 gallon holds three.