Petco Text Logo
Petco Pet Logo

  • Two Easy Ways to Start Earning Rewards!

How many fish can I safely and properly put in a 30-gallon tank?

Updated On September 23rd, 2025

Pet's info: Fish | Unknown - Fish | Male | 1 month and 27 days old | 0.02 lbs

How many fish can I put in a 30 gallon tank? I currently have 4 ghost catfish, a Columbian tetra, 3 neons, 2 medium fantail goldfish and a large fantail goldfish. I want 2 rainbowfish and a cory catfish.

2 Answers

Most Helpful Answer

Image profile

Answered By Andrea M. Brodie, DVM

Veterinarian

Published on March 29th, 2018

The rule of thumb is 1.5" of fish per gallon of tank. So estimate the length of each fish you have, add them all and divide by 1.5. This will give you the size tank you will need in gallons. In a 30 gallon tank you can keep 45 inches of fish (i,e, 45 fish, each 1 " long or 30 fish , each 1.5" long, etc. Do not forget to leave some space for growth of fish.

Vote icon

1Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Image profile

    Answered By Angel Alvarado, LVT

    Licensed Veterinary Technician

    Published on October 30th, 2017

    For small bodied fish (tetras, minnows, guppies, etc) the general "one inch of fish per gallon" rule will likely be fine. For larger bodied fish (goldfish, plecos, Oscars, etc), it should be closer to one inch of fish per 3 gallons of water. Always use the full grown adult size when deciding how many fish to keep. Take into account schooling fish as well which should be kept on groups of at least 5-6 fish.

    Vote icon

    3Pet Parents found this answer helpful

See More Answers

Related Questions

Petco Pet Education Center
Health & Wellbeing
setting up my first ever freshwater fish tank, need to know how many fish should I put in my 55 gallon fish tank,
For small bodied fish (tetras, minnows, guppies, etc) the general "one inch of fish per gallon" rule will likely be fine. For larger bodied fish (goldfish, plecos, Oscars, etc), it should be closer to one inch of fish per 3 gallons of water. Always use the full grown adult size when deciding how many fish to keep. Take into account schooling fish as well which should be kept on groups of at least 5-6 fish.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
What type of saltwater fish can I have in a 10 gallon tank
Thanks for reaching out, the rule of thumb is 1" of fish per 3 gallons, but smaller tanks are very difficult to keep stable, and saltwater fish are easily stressed by environmental fluctuations (salinity, temperature, dissolved oxygen). Good luck.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
what is the maximum amount of goldfishes i can safely keep in a 32 litres fish tank? i dont want to overcroud the tank
Thanks for reaching out about your fish. Typically, most recommendations are 1" of fish per 3 liters of water. The better the filter system, the better the water quality and the more biomass can be handled. Remember, fish grow and therefore the biomass will increase. Good luck.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
We recently bought a 20 gallon fish tank for our house. The tank is currently only holding 16 gallons of water. We currently have 11 fish and 2 snails in the aquarium, totaling to 16 inches of fish (if you count the snails as fish). That’s following
Adding more fish would likely cause overcrowding. This, in turn, could lead to stress, illness and aggression. You are probably at or very close to maximum capacity, especially if you have fish that are still growing.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
is a 10 gallon tank good for 7 betta fish
Hi there! The general rule of thumb is 1 gallon for each inch of fish, so I think that you may need a bigger tank. If the bettas are 2 inches each, they each require 2 gallons of water, making the minimum tank size 14 gallons. Since male bettas can be territorial and aggressive, I highly recommend a larger than normal tank with lots of hiding places for 7 fish (at least 20-25 gallons). You should also watch them very carefully for fighting, and have a backup plan in case any of them need to be separated. Good luck!
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Hi I currently have 2 young goldfish, 1 Young zebra danio, and one black mystery snail! I own a 5.5 gallon tNk for my current fish and I know it isn’t big enough since I know hat goldfish can grow to a large size. What would be a suggested size gallo
The goldfish can get very big and may require a significantly larger tank as they grow and grow. As a rule of thumb, you need 1 gallon of water per inch of body length of fish. So if you have three 1 inch fish, you will need 3 gallons of water. I suspect you are at your max already in the smaller tank. Just so you know, most people do not have goldfish in tanks with tropical fish. You may consider getting two tanks One for your cold water fish like the goldfish, and one for your tropical fish that require a warm water temperature. For the goldfish I would suggest a minimum of a 20 gallon tank. For the Danio, I suggest to get a few more of these as they are schooling fish and a 10 gallon would be just fine. I hope this is helpful and please feel free to post any additional questions.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I have a 26 gallon tank which have 1 adult Texas fish, 3 adult silver sharks and 2 small 3'' tiger Oscars. I have brought another tank of about 10 gallons which have only 1 loach in it. How can I arrange the fishes in between two tanks so that all ca
All these fish can grow quite large. The loach would be the "smallest" at about 6 to 8 inches when full grown. The Oscars can reach lengths of 18 inches and the Texas cichlid and sharks can reach a foot in length. All these fish will require much larger tanks than the ones you have now. The three Oscars alone would do best in a 125 gallon aquarium MINIMUM. The others may thrive in 55 to 75 gallon tanks. To leave them in small tanks will cause stress, aggression and likely infection.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
Can platties, Black mollies, pleco, and neon tetra all be kept together in a 20 gallon tank?
In general these fish can all be housed together safely. The one thing to keep in mind is the amount of space needed per fish to maintain a safe and healthy environment. Each 1in of fish needs 1 gallon of water. So in a 20 gallon tan you can have 20 inches of fish. The Pleco is the only one I have concerns with as some varieties can grow quite large. Check with your local pet shop as to what needs best suit this type of fish or what type of fish suit your tank best.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
What is the best sizes tank to get for 3to4 bubble eye goldfish? I haven’t brought them yet.
Hi, and thanks for your question. There is a general rule about it which is a rough estimate not to overcrowd your aquarium and avoid excessive production of feces and organic debris. The rule is one Inch per gallon, so in 10 gallons there should be ideally 10 inches of fishes in total. You should consider as well the presence of plants and gravel and any other sort of things, which decrease the water volume of 5-10% (so 10 liters are actually 9-9.5). This rule does not consider modern filtration systems. These fish suffer genetically from a certain grade of visual impairment, so overcrowding (especially competition for food) is not recommended. At the same time, please consider as well that schooling fish (like they are) should be kept in numbers, which means more space will be needed, so be generous.
Updated on September 24th, 2025
Petco Pet Education Center
Health & Wellbeing
I want Angel Alvarado to answer this question. What fish can i put in a 3 gallon tank besides shrimp. If I have to get neon tetras please tell me how to change their water. Thanks
The small size will limit the species of fish as well as the number. White Cloud Minnows or Guppies would do fine in a small tank. You could keep no more than 2 or 3 fish total. If you are looking for company for your Betta, the same species can be kept. Other options include Otocinclus (Otos), Corys, Platys or Harlequin Rasboras. Again, no more than one or two in addition to the Betta. Water changes for any tank are simple. Change no more than 30% total volume at a time. Use a water conditioner to remove harmful chemicals and make sure the water is temperature matched to prevent stress or shock. Rinse the filter in tank water, not tap water, to preserve beneficial bacteria. Vacuum the substrate every couple of weeks.
Updated on September 24th, 2025
image
Have A Vet Question?

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

Book Now

Sponsored