What’s The Best Aquaponics Fish To Plant Ratio?

Growing healthy plants through the use of fish waste is an excellent way to generate a bumper crop. Whether you’re intending to grow tomatoes or marijuana this approach can really make your life easier.

However, there are several factors you need to get right before you can start successfully running your aquaponics system.

Understand Aquaponics

The first is understanding the different parts of your aquaponics system:

  • Fish Tank

You need somewhere to keep your fish. This should not be where the fish can access your plant roots. If they can they may nibble them and will produce waste that could actually be harmful to the plants; their solid waste can coat the plant roots preventing them from being able to absorb nutrients.

Having a separate tank will also make it much easier for you to create the perfect environment for your fish; which is different to the one that your plant’s need to flourish.

fish farm with aquaponics

  • Pump

The water moves from the fish tank to the plant base. You can have your plant roots soaking in the water or you can build a clay base above the water; allowing the plants to absorb what they want as and when they want.

Of course, to move the water from one tank to the other you’ll need a pump. Gravity will not be able to do this by itself!

You’ll need to choose the pump according to the size of your fish tank; this will tell you how much water you need to pump. The general consensus is that the entire volume of your fish tank should be pumped around the system every hour.

Purchase your pump according to its specs and the size of your set-up.

  • Filter

Technically a filter should not be necessary as the bacteria in the water will convert the fish waste into nitrates for the plants. However, this process may not always be successfully completed; allowing solid waste particles to travel through the system potentially blocking it up.

A filter can ensure that the larger waste particles are removed; this will prevent the system from becoming clogged.

  • Plant Base

As already mentioned you can have the roots of your plants in your water or you can create a base to house them. Either way, they can produce successful results.

Stocking The Fish

Once you understand all the elements that are involved you’ll be able to decide how big the plant bed is going to be and, therefore, how big the tank will need to be.

A good starting point is to add 1 fish per 5 gallons of tank water. If you don’t know the size of your tank then simply multiply the height, width, and length of your tank in feet. The answer you get is the size of your tank in square feet.

Simply take this figure and multiply it by 7.48; this will tell you how many gallons of water you have. Divide this answer by 5 and you’ll have the approximate number of fish you need for your tank.

tilapia fish

However, before you rush out and purchase all the fish you need to consider the number of plants you intend to grow and the size of your fish. This guide to fish numbers is based on adult fish. If you are purchasing baby fish then you need to base your calculation on the number of full-grown fish you need and then buy half of them.

As your plants start to grow you can increase the number of fish you have until you reach your target fish number. If you put all the fish in when the plants are very young then they will be swamped with nutrients, and be unable to process them all.

The alternative is to look at how many plants you intend to grow.

To do this you’ll need to calculate your growing area by multiplying your length and width. This will give you the square footage of your growing area. You can use the same figure as the number of fish you need.

For example, a plant bed of 4 feet by 4 feet will yield 16 feet of growing space. This equates to 16 pounds of mature fish. As each fish requires 5 gallons of water your tank will need to be a minimum of 16 x 5; that’s an 80-gallon tank.


It is important to note that while this is an accurate calculation every system is different. You should assess what you are intending to grow and then create the number of fish that you believe will produce the right amount of waste. The above calculations should help.

You can then add your fish and monitor the water carefully to ensure the nutrient levels are remaining high while the plants appear to be healthy.

It is important to note that your plant beds should be allowed to drain and then be flooded. This is the best way of getting oxygen into the water to look after the fish. Ideally, use an electronic timer hooked up to your pump and then allow the pump to run for 15 minutes with a 45-minute break between pumping session.

You should also consider how steep the hill is between the fish tank and the plant beds. If it is steep you may need to purchase a more powerful pump. It needs to pump a volume of water equivalent to all the water in the fish tank, and it needs to be able to do this in just 15 minutes!

The Bottom Line

It is important to be aware that you will probably have male and female fish in your system. This can result in you needing to make an allowance for baby fish in the future.

You should also consider the type of fish you are using; not all fish produce the same quality or volume of waste. You’ll soon notice if your plants are looking undernourished; this should be your trigger to add more fish.

The real trick to getting this balance right is to adopt the basic principal supplied in this article and then monitor your progress until you get what works best for you.

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