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Aquarium stocking calculator

This calculator sizes communities by adult tank minima, schooling, and waste. It does not use the inch-per-gallon rule, which counts a 6-inch goldfish and six 1-inch tetras as the same load. The goldfish makes far more waste. Enter the tank you actually have, pick freshwater or saltwater, and your experience level.

Cycle first. How to cycle a fish tank covers the fishless method and the done signal. Then use the tool below for conservative ideas, not a shopping list of everything that could theoretically fit.

Size-specific guides: stocking a 10-gallon tank, stocking a 20-gallon tank, stocking a 29-gallon tank, stocking a 40-gallon breeder, stocking a 55-gallon tank.

Frequently asked questions

Is this the inch-per-gallon rule?+

No. Inch-per-gallon treats a 10-inch oscar like ten 1-inch tetras. This calculator sizes communities by adult tank minima, schooling needs, and a conservative waste budget from the species we actually write about.

What is an aquarium stocking calculator for?+

It turns tank gallons, freshwater or saltwater, and your experience into a few conservative community ideas, plus species that fit and ones to skip. Use it before you buy, not after the store bag is in the car.

Can I mix every species that fits?+

Usually no. Goldfish are coldwater. Oscars eat tank mates. Male bettas may hunt. Pick one example community, not a shopping list of everything that could theoretically survive.

Do I still need to cycle?+

Yes. The calculator assumes a cycled, filtered tank and adult fish. Read how to cycle a fish tank before you buy livestock.

What fits in a 5-gallon tank?+

One male betta, about ten cherry shrimp, or a nerite snail. A betta with one nerite also passes the waste check. Schools and bottom dwellers need a bigger tank.

Stocking a 5-gallon tank

Plan a tank

Rated gallons, not the water line after gravel. Results update as you change the fields.

Water
Experience

20 gal · Freshwater · New to the hobby

Example communities

Pick one idea. Do not stack every species that could theoretically survive. Counts assume adult fish in a cycled tank.

  • Betta centerpiece

    One male in a planted 20 is easier to keep stable than a 5. Do not add a school unless he ignores other fish.

    • 1 × Betta (Betta splendens)One male. Heated, filtered, not a vase. Two males is a fight.

  • Neon and peppered cory community

    Midwater school plus a bottom group. That is a common, conservative 20-gallon community, not inch-per-gallon math.

    • 11 × Neon tetra (Paracheirodon innesi)A school, not a pair. Dimmer light and stable, clean water.
    • 6 × Peppered cory (Corydoras paleatus)Bottom school on sand. Six is a starting group, not a display pair.

  • Zebra danio school

    One active midwater school in a 20-long. Leave an open swimming lane and keep a tight lid.

    • 11 × Zebra danio (Danio rerio)A school of six or more. They want length more than height.

  • Male guppies with cories

    Livebearers up top, a cory group on sand. Keep the guppies male-only so the bioload does not explode.

    • 5 males × Guppy (Poecilia reticulata)Males only unless you want fry and a ballooning bioload.
    • 6 × Peppered cory (Corydoras paleatus)Bottom school on sand. Six is a starting group, not a display pair.

    Mixed-sex guppies will outpace this plan.

  • Platy group

    A small hard-water livebearer group. Fifteen gallons is the floor; twenty is kinder once fry appear.

    • 6 × Platy (Xiphophorus maculatus)Hard-water livebearers. Mixed sexes mean fry, so plan water changes.

    Mixed sexes will produce fry and raise the bioload.

  • Platies with cories

    Hard-water livebearers midwater and a peppered cory group on sand. Match the water to the platies, not soft Amazon numbers.

    • 6 × Platy (Xiphophorus maculatus)Hard-water livebearers. Mixed sexes mean fry, so plan water changes.
    • 6 × Peppered cory (Corydoras paleatus)Bottom school on sand. Six is a starting group, not a display pair.

    Mixed-sex platies will add fry. Soft, acidic water is a poor match.

  • Single bristlenose pleco

    One Ancistrus on wood in a long footprint. Twenty gallons is the floor; leave midwater for a small school only if the bioload stays honest.

    • 1 × Bristlenose pleco (Ancistrus spp.)One adult Ancistrus. 20-long is the floor; 29–30 is comfortable. Not a janitor.

    Not a common pleco. Not a pair tank. They still need wafers and water changes.

Also a possible fit

Species pages that meet this tank size. Read the profile before you mix them with anything else.

  • Freshwater · Beginner · min 15 gal

    8 × Black neon tetra

    Hyphessobrycon herbertaxelrodi

    A school of 6 or more, eight to ten in a planted 20. Takes ordinary tap water better than neons.

  • Freshwater · Beginner · min 15 gal

    8 × Glowlight tetra

    Hemigrammus erythrozonus

    A school of 6 or more, eight to ten in a 20. Dark substrate and dim light bring out the stripe.

  • Freshwater · Beginner · min 20 gal

    6 × Harlequin rasbora

    Trigonostigma heteromorpha

    A school of 6 to 10 in a planted 20. Calm midwater fish and plant-safe.

  • Freshwater · Beginner · min 20 gal

    10 × Celestial pearl danio

    Danio margaritatus

    A group of 10 to 15 spreads out the male sparring. Food small enough for one-inch mouths.

  • Freshwater · Beginner · min 10 gal

    15 × Ember tetra

    Hyphessobrycon amandae

    A school of 10 or more. Ten gallons for embers alone, twenty if you mix in other fish.

  • Freshwater · Beginner · min 10 gal

    15 × Chili rasbora

    Boraras brigittae

    A school of 10 to 12 or more. Soft acidic water, gentle flow, and micro foods.

  • Freshwater · Beginner · min 10 gal

    2 × Honey gourami

    Trichogaster chuna

    One adult in a planted 10, a calm pair in a 20. Do not house with a male betta.

  • Freshwater · Beginner · min 20 gal

    1 × Pearl gourami

    Trichopodus leerii

    One in a 20 long, a pair or one with a school in a 29. Warm air under a close lid.

  • Freshwater · Beginner · min 10 gal

    1 × Dwarf gourami

    Trichogaster lalius

    One male per tank. A 10 for him alone, a 20 for a school or two females.

  • Freshwater · Beginner · min 20 gal

    6 × Cherry barb

    Rohanella titteya

    Six or more so males color up and any nipping stays in the group.

  • Freshwater · Beginner · min 5 gal

    17 × Cherry shrimp

    Neocaridina davidi

    Start a colony with 10 or more. Shrimplets get eaten in almost any community, and copper wipes a colony.

  • Freshwater · Beginner · min 20 gal

    3 × Amano shrimp

    Caridina multidentata

    A crew of 3 to 6 in a planted 20. They starve in a spotless tank without veg wafers.

  • Freshwater · Beginner · min 5 gal

    3 × Nerite snail

    Neritina / Clithon / Vittina (trade mix)

    About one snail per 5 to 10 gallons. Needs a tight lid. Keep copper out of the tank.

  • Freshwater · Beginner · min 5 gal

    2 × Mystery snail

    Pomacea diffusa

    About one snail per 5 to 10 gallons. Needs a lid with an air gap. Copper meds kill them.

  • Freshwater · Beginner · min 10 gal

    7 × Endler's livebearer

    Poecilia wingei

    Start about one male to two or three females. Hard, alkaline water. Expect fry.

  • Freshwater · Beginner · min 20 gal

    1 × Molly

    Poecilia sphenops

    Hard, alkaline water. Mixed sexes mean fry. Sailfins want 30 gallons or more.

  • Freshwater · Beginner · min 10 gal

    14 × Pygmy cory

    Corydoras pygmaeus

    A group of 8 or more on fine sand. Gentle flow, small sinking foods, and a covered intake.

  • Freshwater · Beginner · min 20 gal

    6 × Kuhli loach

    Pangio spp.

    A group of 6 or more on sand. Sponge-safe intakes and a tight lid.

  • Freshwater · Beginner · min 10 gal

    11 × White cloud mountain minnow

    Tanichthys albonubes

    Six or more at 64 to 72°F, often without a heater in a cool room.

Skip for this tank

  • Cardinal tetra — Intermediate care. Cycle first and get comfortable testing water.
  • Rummy-nose tetra — Intermediate care. Cycle first and get comfortable testing water.
  • Swordtail — Tight. The swordtail page says 20 gallons can work, but 29 is better.
  • Goldfish — Adults want about 30 gallons, not 20. Intermediate care. Cycle first and get comfortable testing water.
  • Angelfish — Adults want about 30 gallons, not 20. Intermediate care. Cycle first and get comfortable testing water.
  • Bolivian ram — Tight. The bolivian ram page says 20 gallons can work, but 29 is better.
  • Pea puffer — Intermediate care. Cycle first and get comfortable testing water.
  • Siamese algae eater — Adults want about 30 gallons, not 20.
  • Otocinclus — Intermediate care. Cycle first and get comfortable testing water.
  • Oscar — Adults want about 75 gallons, not 20. Advanced husbandry. Wait until you are ready for the mess.

Gear that belongs with this

Filter, heater, and a real test kit. Links go to notes on this site — not a shopping cart.

Still cycling? How to cycle a fish tank · Beginner freshwater setup · Stocking a 20-gallon tank