Guest Article from

One factor of our project at UT that we would like to improve upon is the ecological balance of an aquaponics system. We would like to thank Nick from for writing this guest article over that subject for us! Enjoy!


Aquaponics: Getting The Ecological Balance Right

When you consider an aquaponics system, you’re choosing to grow plants in an environment that can be controlled but remains environmentally friendly. Done properly, an aquaponics system can increase crop and fish yield, therefore providing a greater supply of food without disturbing the ecological balance.

But there are several factors involved in getting the ecological balance right. It’s important that you understand these before you start setting up your system.

Getting the ecological balance right means a better return on your investment.

We should strive for ecological balance in our aquaponics system because it will increase the crop yield and growth of the fish.

Aquaponics Water Cycle Maintenance


Getting the Fish Numbers Right

Put too many fish in your tank and you’ll have more nutrients than your plants can handle. This will effectively destroy the balance of the water and can be harmful to your fish.

Of course, too few fish and you won’t have enough nutrients for your plants.

In fact, fish numbers and plant numbers are intrinsically linked.

For fish you should aim to have around 4 gallons of water per fish. Therefore, if you have a 40 gallon tank you can have 10 fish. (150 litres for 10 fish)

However, it is important to note that this is the full grown weight of the fish. If you’re stocking your system with babies, then you’ll need to know what size and weight they will grow to and base your fish calculations on this.

Generally, it’s advised to have a ratio of 1/3. This means 0.3 pounds of fish per square foot of floating raft area.

Choosing the amount of crops

The real question is how many plants would you like to grow?

In general terms you’ll need 1lb of fish for every square foot of growing space.

This means you need to know what density your preferred crop likes. For example you can grow approximately 1 lettuce in a square foot of grow space, assuming we work with floating rafts.

Once you know how many crops you can grow in 1 square foot of space, you can work out how many plants you would like to produce. This will then give you the grow space you require and the number of fishes. For more information check out this website:

For example, you want to grow 40 lettuces

You’ll need 40 square feet of grow bed for your lettuces at 1 per square foot. (3.7m²)

If we multiply 40 by 0.3 we will become 12. We need 12 pounds of fish to have a healthy system.

Of course, you will start out with a lower number because the fish will grow over time.

To stock 12 fish, you’ll need 50 gallons of water; that defines the size of your tank! (180 liters)

Here are some other common plant densities:

  • Basil – between 3 and 12 plants per square foot
  • Cauliflower – between 1 and 2 plants per square foot
  • Cucumbers – between 1 and 2 plants per square foot
  • Eggplant – between 1 and 2 plants per square foot
  • Peppers – between 1 and 2 plants per square foot
  • Cabbage – between 2 and 3 plants per square foot
  • Swiss Chard – between 5 and 7 plants per square foot

Water Quality & Nutrients To Keep The System Balanced

The fundamental principle of aquaponics is that you feed the fish; they provide nutrients for the plants which provide clean water for them.

In a perfect system that’s all you need to do; feed the fish.

Of course, this is not an advisable approach. It is essential to test the water on a regular basis. That’s why you should perform these tests:


  • Dissolved oxygen level
  • Temperature
  • pH level



  • Ammonia levels
  • Nitrates
  • Nitrites
  • Alkalinity


In the average aquaponics system, in order to keep your setup healthy for your plants and fish, you should keep the temperature between 65° – 85° F.

You’ll also need to keep the pH between 6 and 7. If it is too low you can add a base mixture of calcium hydroxide, potassium bicarbonate, calcium chloride, or sodium bicarbonate.

Ammonia should be less than 1ppm, as should the nitrite levels. If these are starting to climb, then you need to reduce the amount of fish food you’re using.

Nitrate should be between 5 and 150 ppm.

Dissolved oxygen should be less than 5 ppm.

Of course the plants you’re growing and the fish you’re keeping may affect these parameters. It’s important to be aware of what environment suits them best.

It is worth noting that once you get the levels right, they are usually good at staying there by themselves.

The Effects Of Additional Organisms

In theory an aquaponics system has no pests or other life forms that can cause an issue for your new setup. However, the truth is that worms, snails and other small organisms are often present in the growing media you’re using.

Fortunately you don’t need to spend hours removing every one. Snails in particular are very good at consuming any extra food you’ve put into your system. This will help to retain the balance of your aquaponics system.

In addition most fish will actually consume snails if they are hungry. This means the snails are a great way of ensuring your fish are fed; even if you forget.

All you need to do is add a few snails to your tank. If you’re over feeding your fish the snail population will grow rapidly. If you’re underfeeding then the snails will quickly reduce in numbers; it’s a great way to get your fish food level right.

Malaysian Trumpet Snail


You can also tell if your system has too much calcium in the water. When the snails die, their shells go to the bottom of the tank; they are full of calcium salts. Live snails can eat these shells to get their own calcium. However, if the shells are piling up you have too much calcium salts in your setup. This can be bad for your plants.

The best snails to get are the Malaysian Trumpet and the Rams Horn Snails. These multiply quickly giving you a good indication of your water quality and helping to maintain the balance in your aquaponics setup.  

The worm is useful in traditional planting as it turns the soil and consumes excess waste from fish and plants; helping the plants to have an adequate supply of food.

Worms can even be beneficial to your plants to prevent them from getting diseases or bothered by pests! In fact worms even produce antibiotics that kill organisms in the soil; making it an almost sterile environment.

Of course, if you’re adding any worms, snails or other bacteria to your set-up it’s important to make sure they are fully cleaned first. You want to improve the aquaponics environment not make it worse!