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Best fish for a 40 gallon tank

A 40 gallon breeder is wide and shallow, so it has the floor space for big groups of bottom dwellers and a calm community above them.

Checked by our tank model as a starter group in an empty, cycled 40G Breeder (91 × 46 × 41 cm) with a filter rated for it. One group per tank; mix species with the planner.

Possible, with care

  1. Neon tetra

    Paracheirodon innesi
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 8 · 1.2 in · 17+ gal · 70–77°F · pH 5–7

  2. Harlequin rasbora

    Trigonostigma heteromorpha
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 8 · 1.4 in · 17+ gal · 73–81°F · pH 6–7

  3. Fancy guppy

    Poecilia reticulata
    With care

    GH 8 dGH is outside the Fancy guppy range 8–25 dGH.

    group of 3 · 1.4 in · 13+ gal · 75–81°F · pH 7–8

  4. Panda corydoras

    Corydoras panda
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 6 · 1.6 in · 17+ gal · 72–77°F · pH 6–7.2

  5. Otocinclus

    Otocinclus vittatus
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 6 · 1.4 in · 17+ gal · 72–79°F · pH 6–7.2

  6. Cherry shrimp

    Neocaridina davidi
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 10 · 1.6 in · 4+ gal · 72–75°F · pH 6.5–7.8

  7. Betta

    Betta splendens
    With care

    Betta: turnover 3.7/h is above the comfortable 3/h.

    2.8 in · 11+ gal · 72–86°F · pH 6–7.5

  8. Angelfish

    Pterophyllum scalare
    With care

    Angelfish: tank height 41 cm < 45 cm needed.

    3.5 in · 32+ gal · 77–84°F · pH 6–7

  9. Tiger barb

    Puntigrus tetrazona
    With care

    Tiger barb: turnover 3.7/h is below 4/h.

    group of 6 · 2.2 in · 32+ gal · 72–79°F · pH 6–7.5

  10. Amano shrimp

    Caridina multidentata
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 3 · 2 in · 7+ gal · 72–77°F · pH 6.5–7.5

  11. Black neon tetra

    Hyphessobrycon herbertaxelrodi
    With care

    Turnover 3.7/h is below the recommended 4/h.

    group of 8 · 1.4 in · 23+ gal · 73–81°F · pH 5.5–7.5

  12. Blood parrot cichlid

    hybrid
    With care

    Turnover 3.7/h is below the recommended 4/h.

    7.9 in · 36+ gal · 72–82°F · pH 6.5–8

And 75 more in the species catalog.

Too much

  1. Black widow tetra

    Gymnocorymbus ternetzi
    Avoid

    pH 7.2 is outside the Black widow tetra range 6.0–7.0.

    group of 12 · 2.4 in · 22+ gal · 68–79°F · pH 6–7

  2. Blue dolphin cichlid

    Cyrtocara moorii
    Avoid

    Temperature 76°F is outside the Blue dolphin cichlid range 77–84°F.

    group of 3 · 9.8 in · 80+ gal · 77–81°F · pH 8–8.5

  3. Chinese algae eater

    Gyrinocheilus aymonieri
    Avoid

    Chinese algae eater: tank length 91 cm < 168 cm needed.

    group of 6 · 11 in · 95+ gal · 72–79°F · pH 6–8

  4. Clown loach

    Chromobotia macracanthus
    Avoid

    pH 7.2 is outside the Clown loach range 5.0–7.0.

    group of 6 · 15.7 in · 202+ gal · 75–86°F · pH 5–7

  5. Common pleco

    Pterygoplichthys pardalis
    Avoid

    Amazon sailfin catfish (common pleco): needs a 650 L tank, this one is 172 L.

    22.8 in · 203+ gal · 77–82°F · pH 7–7.5

  6. Demasoni

    Chindongo demasoni (syn. Pseudotropheus demasoni)
    Avoid

    pH 7.2 is outside the Demasoni range 7.6–8.8.

    group of 6 · 3 in · 64+ gal · 75–82°F · pH 8.2–8.5

  7. Discus

    Symphysodon aequifasciatus (species complex)
    Avoid

    Temperature 76°F is outside the Discus range 79–86°F.

    group of 5 · 5.5 in · 80+ gal · 79–86°F · pH 5–7

  8. Fairy cichlid

    Neolamprologus brichardi
    Avoid

    pH 7.2 is outside the Fairy cichlid range 8.0–9.0.

    group of 2 · 3.5 in · 34+ gal · 73–79°F · pH 8–9

  9. Golden mbuna

    Melanochromis auratus
    Avoid

    pH 7.2 is outside the Golden mbuna range 7.6–8.8.

    group of 4 · 4.3 in · 64+ gal · 75–82°F · pH 7.6–8.8

  10. Iridescent shark

    Pangasianodon hypophthalmus
    Avoid

    Iridescent shark: needs a 14580 L tank, this one is 172 L.

    51.2 in · 4532+ gal · 72–79°F · pH 6.5–7.5

  11. Kuhli loach

    Pangio semicincta
    Avoid

    pH 7.2 is outside the Kuhli loach range 3.5–7.0.

    group of 6 · 3.9 in · 17+ gal · 70–79°F · pH 3.5–7

  12. Leopard sailfin pleco

    Pterygoplichthys gibbiceps
    Avoid

    pH 7.2 is outside the Leopard sailfin pleco range 5.0–7.0.

    19.7 in · 187+ gal · 77–86°F · pH 5–7

And 51 more in the species catalog.

How many fish fit in 40 gallons?

The old inch-per-gallon rule ignores body shape and group size. We estimate bioload from adult mass and water temperature, compare it with what the filter and weekly water changes remove, then add the space each species needs to swim and school.

The list above checks one species at a time. To mix several, add them to your own tank: the planner checks every pair and the combined load.

Every tank is different. Set yours up once (size, water, who already lives there) and each species is checked against it.

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