TankBud

Best saltwater fish for a 20 gallon tank

A 20 gallon saltwater tank fits a pair of clownfish with one or two small fish beside them and a clean-up crew. Ocellaris and percula clownfish, firefish, the yellow watchman goby and the tailspot blenny all list a 20 gallon (75 liter) minimum. Every fish in the list is widely sold, rated for community tanks and lists a minimum tank of 20 gallons or less. The three plans below are reef tanks checked in the stocking calculator, which counts adult size and each species' minimum tank.

Keeping a freshwater tank? Freshwater fish for a 20 gallon tank →

At a glance

Tank size
5–20 gal
5 gal (19 L) to 20 gal (75 L); half the list needs 20 gal (75 L) or more
Temperature
72–79°F
22–26°C, most of the list
pH
8.1–8.4
Most of the list
Temperament
10 peaceful
5 mostly peaceful
Reef safety
13 reef safe
2 reef safe with caution

15 species

At this size

What a 20 gallon reef holds

Ocellaris and percula clownfish list 20 gallons (75 liters) and grow to 3.1 inches (8 cm). A pair fits with room for one more small fish. The firefish and the yellow watchman goby list 20 gallons too and reach 3.5 inches (9 cm). The tailspot blenny and the yellow cardinalfish stay at 2.4 inches (6 cm) or less. The neon goby and the yellow clown goby list 11 gallons (40 liters).

Stocking plans

Three ways to stock a 20 gallon tank

Each plan below ran through the stocking calculator, which reads every fish at its adult size against its minimum tank. Open one to change the counts or swap in your own fish.

By the numbers

Smallest

  1. 01
    Blackbelly dwarfgoby (Eviota atriventris)

    Blackbelly dwarfgoby

    Eviota atriventris

    0.8 in (2 cm)
  2. 02
    Queensland dwarfgoby (Eviota queenslandica)

    Queensland dwarfgoby

    Eviota queenslandica

    0.9 in (2.4 cm)
  3. 03
    Barber goby (Elacatinus figaro)

    Barber goby

    Elacatinus figaro

    1.6 in (4 cm)
  4. 04
    Broadstripe cleaner goby (Elacatinus prochilos)

    Broadstripe cleaner goby

    Elacatinus prochilos

    1.6 in (4 cm)

Largest

  1. 01
    Firefish (Nemateleotris magnifica)

    Firefish

    Nemateleotris magnifica

    3.5 in (9 cm)
  2. 02
    Lined blenny (Ecsenius lineatus)

    Lined blenny

    Ecsenius lineatus

    3.5 in (9 cm)
  3. 03
    Purple firefish (Nemateleotris decora)

    Purple firefish

    Nemateleotris decora

    3.5 in (9 cm)
  4. 04
    Yellow watchman goby (Cryptocentrus cinctus)

    Yellow watchman goby

    Cryptocentrus cinctus

    3.5 in (9 cm)

Most peaceful

FAQ

Common questions

How many fish can go in a 20 gallon saltwater tank?

Three or four small fish and a clean-up crew fill a 20 gallon reef. The plans above hold a clownfish pair with a firefish, or a watchman goby, two neon gobies and a tailspot blenny. Run your own mix through the stocking calculator, which checks each fish against its minimum tank.

Can clownfish live in a 20 gallon tank?

A pair of ocellaris or percula clownfish can, since both list 20 gallons (75 liters). Clark's, tomato and cinnamon clownfish list 30 gallons (115 liters), and the maroon clownfish lists 40 gallons (150 liters).

Can a tang live in a 20 gallon tank?

No. The tomini tang is the one tang on these pages, and it lists 70 gallons (265 liters). The yellow tang lists 100 gallons (380 liters).

Does a clean-up crew count toward stocking?

The stocking calculator counts snails, hermit crabs and cleaner shrimp at a small share of a fish's waste. A cleaner shrimp and five snails barely move the first plan above.

Index

All saltwater fish for a 20 gallon tank

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