How Many Fish Can You Put In A 5 Gallon Tank

Last Updated on July 20, 2021 by Marco C.

How many fish you can put in a 5 gallon tank depends on fish stocking density, target weight per fish, filter capacity, and aeration. A smaller space tank constrains the growth of the fish inside and will not be able to develop larger than the tank. Personally I prefer growing with a smaller tank with low fish stocking density while focusing on the hydroponics unit instead. There are different fishes suited for a 5 gallon tank. Fish stocking density can go anywhere from between 0.125 to 0.417 pounds per gallon (lbs/gal) depending on the practitioner’s preference. First, we must determine the preferred fish stocking density, then we must then ensure that the system can handle the amount of fish in your system.

Fish Species Have Different Behavior, Tolerance Levels, and Target Weight Per Fish Which Will Determine Their Fish Stacking Capacity

Fish species differ in how they adapt to stocking density and the space needed for them to grow comfortably. The first step in determining how many fish you can put in a 5 gallon tank is to have a per fish.

Determining The Target Fish Biomass From Stocking Density Dictates How Many Fish Can Be Put In A 5 Gallon Tank

Each species of fish differs in maximum weight at full-grown or market size. The maximum or harvesting weight dictates your fish stocking density. In a 5 gallon tank, your water level should be at around 70% of the tank size to ensure water does not overflow. This gives you a water volume of 3.5 gallons. Your total fish biomass in the tank is based on the volume of water. Total fish biomass for a 5 gallon tank with 3.5 gallons of water can range from 0.4375 for low-medium stocking densities to 1.45 pounds for high stocking densities. From this total fish biomass, you can then determine how big you want your fish to be at full size. Best fishes for 5 gallon tanks include:

  1. Nile Tilapia
  2. Catfish are a good choice if you choose to just grow one fish as catfishes are extremely territorial and will attack other catfishes in small enclosed spaces.
  3. Freshwater prawns
  4. Koi or carps are a good choice as well although Koi fishes are not for eating
  5. Goldfishes are also an option if you do not plan on harvesting your fishes

Now that you have your total fish biomass and target weight per fish, it is important to determine their survivable water parameters and design your system to allow for livable conditions for the fish.

A High Fish Stocking Density Maximizes The Amount Of Fish Biomass In A Small Tank But Also Puts Stress On The Fishes

Some species like catfish have minimal requirements for dissolved oxygen although are very territorial. Tilapia on the other hand requires minimal dissolved oxygen as well but are less likely to attack fellow fish. More fishes will mean more competition for dissolved oxygen. Without proper aeration and water flow in your system, will lead to fish kills. A high fish stocking density will also increase the amount of nitrogen in the system. If not utilized or converted properly will increase nitrites. Nitrites are dangerous for fish even at a small concentration, leading to brown blood disease.

 dissolved oxygen

After Deciding On How Many Fishes You Put In Your 5 Gallon Tank, It Is Important To Adjust Water Flow, Aeration, and Filtration Capacity

There are different adjustments you will have to make to your system to adjust to a high fish stocking density or a low fish stocking density. These will allow you to maximize the productivity of your system and avoid getting fish kills as well.

First Adjustment You Will Need To Make Will Be To Your Water Flow

Your water flow will need to be higher if you choose to go with a high fish stocking density. Alternatively, your water flow in the system can also be lower with a low fish stocking density. According to Dr. Lennard, for low fish stocking densities below 0.125 lbs/gal, your system will work with a water turnover rate of half the volume of your fish tank water per hour. Fish stocking densities higher than 0.125 lbs/gal require a water flow of 1 fish tank volume per hour.

For a 5 gallon tank, we go back to the water volume of 70% of your tank’s full volume. You will need a water flow rate of 1.75 gallons per hour for low stocking densities. For higher fish stocking densities, 3.5 gallons per hour is recommended. Be careful not to go beyond 3.5 gallons per hour for your water flow rate as this may also cause stress for the fishes.

From Your Water Flow Rate and Fish Stocking Density, We Can Compute Your Filtration Capacity To Avoid Buildup Of Sediments In Your System.

Just like how flow rate must be higher for high fish stocking densities; the same applies to the size of your filter capacity. Your mechanical filter depends on the retention time of your water to allow for sediments to settle for removal. According to Dr. Lennard, your water retention must be 30 mins to 1 hour of your fish tank’s water volume. For a low fish stocking density, your mechanical filter should range from 0.875 gallons to 1.75 gallons. For fish stocking density above 0.125 lbs/gal, it is best to have anywhere from 1.75 gallons to 3.5 gallons. These numbers should be computed from the water volume in the mechanical filter, and not the size of the mechanical filter itself.

More Fishes In The Water Will Require More Aeration Because Of Competition Of Dissolved Oxygen and Increased Amounts Of Nitrogen

As your fish density increases, add more aeration to keep dissolved oxygen at stable concentrations for your fish. More fish will mean more biological oxygen demand for your fish and bacteria, and chemical oxygen demand to convert nitrogen to forms that can be used for plants. Adding air stones and designing your system to have water splashing into different components increases aeration sufficiently. It is best to have an electronic dissolved oxygen meter to measure dissolved oxygen levels regularly and adjust to tolerable levels for your fish.

Before deciding how many fishes to put into a 5 gallon tank, decide on your goal for your aquaponics system. You can maximize your 5 gallon tank for growing fish by having a high fish stocking density. On the other hand, you can use it simply as a constant supply of nitrogen for your plants. On deciding the best fish for your 5 gallon tank, determining your target weight and stocking density dictates what fish can grow in those conditions.

Learn more about: Raising Salmon At Home Using Aquaponics

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