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Best fish for a 125 gallon tank

A 125 gallon (183 cm) takes the fish that outgrow everything else: oscars, larger cichlids and big plecos, with room to spare.

Checked by our tank model as a starter group in an empty, cycled 125G (183 × 46 × 53 cm) with a filter rated for it. One group per tank; mix species with the planner.

Good fits

  1. Tiger barb

    Puntigrus tetrazona
    Fits

    Bold, fast barbs that nip fins; great in a busy group of ten, a poor match for slow or long-finned fish.

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

  2. Bristlenose pleco

    Ancistrus cf. cirrhosus
    Fits

    The go-to glass cleaner: a compact 5-inch pleco with bushy whiskers on the males that needs a cave and vegetables, not just algae.

    4.9 in · 17+ gal · 70–79°F · pH 5.5–7.5

  3. Rainbow shark

    Epalzeorhynchos frenatum
    Fits

    An olive 'shark' with red fins, most often sold in its albino form; territorial toward lookalike bottom fish and best kept alone.

    5.9 in · 76+ gal · 75–79°F · pH 6.5–8

  4. Red-tailed black shark

    Epalzeorhynchos bicolor
    Fits

    A velvet-black 'shark' with a red tail; beautiful but territorial, chasing lookalike bottom fish and its own kind as it ages.

    4.9 in · 76+ gal · 72–79°F · pH 6.5–7.5

  5. Siamese algae eater

    Crossocheilus oblongus
    Fits

    A slim silver fish with a black stripe and one of the few that eats black beard algae; grows to about 6 inches and loves to jump.

    5.9 in · 95+ gal · 75–79°F · pH 6.5–8

  6. Congo tetra

    Phenacogrammus interruptus
    Fits

    A large African tetra with shimmering scales and long, feathery fins on the males; peaceful but skittish, so it needs a roomy tank.

    group of 6 · 3.1 in · 34+ gal · 73–79°F · pH 6–7.5

  7. Denison barb

    Sahyadria denisonii
    Fits

    A large, torpedo-shaped barb with a red line along its body; peaceful but very active, needing a long tank with flow and spotless water.

    group of 6 · 4.3 in · 76+ gal · 59–77°F · pH 6.8–7.8

  8. Dwarf chain loach

    Ambastaia sidthimunki
    Fits

    A 2.5-inch loach with a chain-link pattern that shoals near the bottom and in midwater; fits smaller tanks but eats snails and baby shrimp.

    group of 6 · 2.4 in · 23+ gal · 68–86°F · pH 5.5–7.5

  9. Giant danio

    Devario aequipinnatus
    Fits

    Temperature 76°F works for Giant danio, but 72–75°F is ideal.

    group of 8 · 3 in · 76+ gal · 72–75°F · pH 6–8

  10. Neon dwarf rainbowfish

    Melanotaenia praecox
    Fits

    A small rainbowfish with shimmering blue scales and red fins on the males; shy, schooling and in need of open swimming space.

    group of 6 · 2 in · 17+ gal · 73–82°F · pH 6.8–7.5

  11. Yoyo loach

    Botia almorhae
    Fits

    An energetic silver-and-black loach of about 6.5 inches that excels at eating snails but can tear the fins of slow, long-finned fish.

    group of 6 · 6.3 in · 76+ gal · 66–82°F · pH 6–7.5

Possible, with care

  1. Neon tetra

    Paracheirodon innesi
    With care

    Neon tetra: turnover 5.1/h is above the comfortable 5/h.

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

  2. Harlequin rasbora

    Trigonostigma heteromorpha
    With care

    Harlequin rasbora: turnover 5.1/h is above the comfortable 5/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

    Panda corydoras: turnover 5.1/h is above the comfortable 5/h.

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

  5. Otocinclus

    Otocinclus vittatus
    With care

    Otocinclus: turnover 5.1/h is above the comfortable 5/h.

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

  6. Cherry shrimp

    Neocaridina davidi
    With care

    Cherry shrimp: turnover 5.1/h is above the comfortable 5/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 5.1/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: turnover 5.1/h is above the comfortable 5/h.

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

  9. Amano shrimp

    Caridina multidentata
    With care

    Amano shrimp: turnover 5.1/h is above the comfortable 5/h.

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

  10. Black neon tetra

    Hyphessobrycon herbertaxelrodi
    With care

    Black neon tetra: turnover 5.1/h is above the comfortable 5/h.

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

  11. Blood parrot cichlid

    hybrid
    With care

    Blood parrot cichlid: turnover 5.1/h is above the comfortable 5/h.

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

  12. Bronze cory

    Corydoras aeneus
    With care

    Bronze cory: turnover 5.1/h is above the comfortable 5/h.

    group of 6 · 3 in · 23+ gal · 70–81°F · pH 6–8

And 72 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

    Stocking of 162% is above the 150% limit.

    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. 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

  6. 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

  7. 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

  8. 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

  9. Iridescent shark

    Pangasianodon hypophthalmus
    Avoid

    Iridescent shark: needs a 14580 L tank, this one is 446 L.

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

  10. 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

  11. 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

  12. Multies

    Neolamprologus multifasciatus
    Avoid

    pH 7.2 is outside the Multies range 7.5–9.0.

    group of 2 · 1.8 in · 13+ gal · 77–80°F · pH 8–8.5

And 43 more in the species catalog.

How many fish fit in 125 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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