Petco Text Logo
Petco Pet Logo
  • Two Easy Ways to Start Earning Rewards!

    rewards header
    Become a member today!
    Members-only pricing and offers, personalized care notifications, Vital Care points back on every purchase and more!
    Petco Pay LogoBecome a credit card member today!

    Earn 2X Pals Rewards points at Petco
    when you use Petco Pay!

    APPLY NOW
    Learn More About Petco Pay Benefits

20-gallon tank setup: What fish and supplies do I need to get started?

Updated on September 23rd, 2025

I have a 20 gallon tank. I'm thinking of buying +5 fish. Which fish could I buy and what would I need for the fish and tank?

2 Answers

Most Helpful Answer

Angel Alvarado, LVT

Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on November 23rd, 2017

A fish tank will need a filter, a light/hood and a heater. Make sure the filter is rated for at least twice the tank volume. The heater should be adjustable since water temperature will depend on the species of fish.
Good "starter" fish include Tetras, Mollies, Danios or Tetras.
A new tank should be set up and left running empty for several weeks before adding fish. A pinch of flake food can be sprinkled in daily. This "cycling" will allow a population of beneficial bacteria to colonize the tank and filter. These bacteria will break down wastes (ammonia, nitrites and nitrates) which are toxic to fish.
Vote Icon3Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on September 11th, 2017

    At the very least, a 10 gallon tank with a filter, heater, hood and light. Ideally, the tank should be up and running (without fish) until it cycles properly. This means there needs to be sufficient time for beneficial bacteria to colonize the tank and filter to be able to break down wastes, namely ammonia and nitrites and to a lesser degree, nitrates. This can take several weeks to occur.
    You can cycle a tank with fish in it, but it will require daily testing of water chemistry to prevent a toxic build up of ammonia and/or nitrites. Either can kill your fish if not treated.
    Follow this link for a FAQ regarding Glo Fish: https://www.glofish.com/about/faq/
    Follow this link for more about cycling a tank: http://www.firsttankguide.net/cycle.php

    Vote Icon

    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Share

Styled arrow button