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Best fish for a 100 litre / 26 gallon tank

86 species in the library list a minimum of 100L or less (about 26 US gallons). 49 species need more water than that. This page shortlists. It does not replace the tank builder or pair checker.

A 100L is the default “proper community” kit size — room for two calm schools and a bottom crew, or one school plus a bristlenose and dwarf cichlid pair if height and hardscape are honest. Mollies and swordtails finally have bioload room if the water stays hard. What people misread is height: a low 100L is not an angelfish tank even when the litre count looks fine.

Stocking philosophy

100L holds three roles if you stop at three. The fourth fish is how a forgiving tank becomes a weekly crisis.

100L mistakeStocking adult angelfish because the tank is “100 litres.” Most 100L aquariums are too short in height; angels need vertical glass and a tall hardscape plan.

Open tank builder (100L)·Pair checker·All fish

Good first pass

Peaceful, beginner or intermediate care, not predatory. Adult size is capped on very small hubs. Still open each profile.

Beginner-peaceful picks

Beginner care, peaceful, not a fin-nipper, not predatory. Tighter than the list above.

Stocking ideas for a 100L

Starting points in words, not drawings. Nothing here is a buy list. Use the tank builder and pair checker on the real mix.

  • Hard-water livebearer lane

    Mollies or platies with hard alkaline water, a real filter budget, and short-finned neighbours — not neon tetras. Confirm chemistry on both profiles, then simulate bioload in the tank builder.

  • Two schools, one bottom crew

    Two calm midwater schools under 5 cm plus corydoras or a bristlenose, and stop. Height still rules out adult angels. Pair-check across schools before you add the algae crew.

Caution (fits the litres, not a free community pass)

Fin nippers, semi-aggressive fish, advanced care, big groups, or species that may eat smaller tank mates. Can work in a mature, species-appropriate setup. Not a starter mix.

Specialist / high-load (even if min ≤ 100L)

Predatory, aggressive, advanced, large groups, or may-eat-small. Not a typical community-first stock.

Too big for a 100L

Adult angelfish need vertical glass most 100L lids never give. Common plecos, clown loaches, and “temporary” bala sharks still outgrow this class. Soft-water discus plans and hard-water livebearer plans do not share one heater schedule without someone losing.

These species list a higher minimum volume. They belong on a larger hub, not in this tank class.

Common mistakes at this volume

  • Stocking adult angelfish because the tank is “100 litres.” Most 100L aquariums are too short in height; angels need vertical glass and a tall hardscape plan.
  • Running a soft-water neon school and hard-water mollies in the same 100L. Temperament can look fine while chemistry quietly fails one side.
  • Buying the fish at the length you see in the shop, not the adult length on its profile. The shop length is six months old at most.
  • Under-schooling tetras, rasboras, or barbs. The fish look sick during the first week, and the diagnosis is almost always group size, not disease.
  • Mixing fin-nippers with slow or long-finned fish without checking the fin-nipper flags. Most personality clashes you read about online are layout problems with a named scapegoat.
Full suitable list (86) — same min-tank filter as above

Every freshwater species in the library with a min tank of 100L or less. Prefer the sections above for decisions.

Plan a 100L stock

Shortlist from this hub, then run the real mix through the builder before you buy.

Open pair checkerOpen this plan in builder

Equipment for a 100L

A stocked 100L community needs a filter turning over roughly 400 L/h and a heater in the 100-200W range. Undersized filtration is the most common cause of the ammonia spikes that kill week-one stock.

Filter size guide →Heater size guide →Tank setup checklist →

Related guides

Planted tank? Beginner plants · Low-light plants · No-CO2 plants

Other tank hubs

Categories in the suitable list

Common questions about a 100L tank

What fish can I keep in a 100 litre tank?
A 100L can hold three roles if height and chemistry match. Prefer the shortlists over the full suitable dump; adult angelfish still need taller glass than most 100L tanks give.
What is the most common mistake at 100 litres?
Stocking adult angelfish because the tank is “100 litres.” Most 100L aquariums are too short in height; angels need vertical glass and a tall hardscape plan.
What else goes wrong at this tank size?
Running a soft-water neon school and hard-water mollies in the same 100L. Temperament can look fine while chemistry quietly fails one side.
Should I use litres or the tank builder for a 100L stock?
Use this hub to shortlist, then load the real mix into the tank builder and open a pair check for every new species. Volume alone never proves a community works.