Aquaponics with Goldfish

Why aquaponics with goldfish? Three reasons:

  • Justify your goldfish obsession to your curious friends and family.
  • Grow healthy food at home.
  • Reduce or eliminate water changes.

And one more reason: Make your pets give you something for a change.

So what is there to do? Today I’m going to give you an overview of how it works and what you need to get started.

Aquaponics is a very broad subject with volumes devoted to it, so there is no way I can tell you everything you need to know and I encourage you to do more research before you get your system up and running.

With that being said, I have tried my best to put everything I know into this guide.

The aquaponics container

Aquaponics containers come in all shapes, sizes, and colors. Some people use waterers, barrels, or large plastic buckets/tubes.

This prefab pond from Oase is a popular choice:

Although personally I prefer to use a real fish tank to be able to better appreciate the fish from the side:

Anything 10 liters and up can be used for aquaponics, but a smaller tank will not support as much growing medium or fish population.

You can keep 30 to 60 square cm for every 40 liters of fish water, but logically more liters = more fish and more plants.

Related Post: The Best Aquaponics Aquariums

Choice of substrate

Many aquatic facilities opt for gravel, sand, or a bare bottom. The use of some type of substrate is recommended for several reasons:

  • Provides a home for nitrifying bacteria to convert ammonia to nitrite and nitrite to nitrate (nitrate is then used by plants)
  • Provides a more natural home for goldfish, minimizing glare from lights and helping them exercise their natural foraging behavior.
  • It allows you to plant various types of aquatic plants that grow large root systems.

Sand is an aesthetic option and easy to vacuum. However, using goldfish gravel can be a choking hazard if the pieces are too small.

If using gravel, I recommend using the medium to large sized smooth gravel (which looks more like small pebbles) rather than pea sized to avoid this.

These large pebbles are around 1-2 cm which is perfect and you can see here. They are marketed to turtle keepers (because it is larger than typical standard gravel) but goldfish owners also use them in their aquariums.

Make sure you wash the gravel well first. Gravel alone can be difficult to keep clean and can lead to water quality problems.

That’s why I actually recommend making a substrate with gravel Walstad style: with a 2-3 cm layer of soil below a 2-3 cm layer of large gravel on top.

Why? According to the Walstad method:

  • Soil contains bacteria that not only break down nitrite and ammonia, but also nitrates. (This is important as debris tends to fall through cracks in the gravel and can be unsightly if not broken down.)
  • It also has carbonates that stimulate plant growth, both for submerged and aquaponic plants.
  • Stabilizes KH, helping prevent pH drop
  • Soil bacteria break down fish waste and uneaten food into nutrients that can be used by plants.
  • Depletion of minerals in water normally requires changes to the water to replenish it, but the soil continually releases trace elements and minerals into the water over time. This reduces the need for water changes.
  • Soil lasts for years, as plant and fish residues replenish the nutrients they draw from the soil.

Organic potting soil mix is ​​the best way to avoid putting chemical fertilizers in the tank, which can become toxic once submerged in water.

Don’t be afraid to have a lot of submerged plants as well as a lot of plants in your grow bed. Plants provide shelter for your fish, remove excess nutrients, aerate the substrate with their roots, and help with oxygen levels in the water.

It is usually easier to add more fish and feed them more than it is to struggle with the water quality problems of an overpopulated system.

Not having enough waste is rarely the problem for most systems.

In addition, the roots of the plants will prevent pockets of toxic anaerobic bacteria from forming in the substrate, as well as absorbing nutrients created by the decomposition of organic waste.

Without making this substrate, depending on how many plants are growing in your system and how many fish you have, you may or may not end up with 0 nitrate in an established system.

Finally, the gravel is not vacuumed with this method. That would suck up all the precious dirt and undo Walstad’s perfect substrate setup.

Did you hear right? No need to vacuum the gravel!

By adding the soil/gravel substrate it seems that a self-sufficient aquarium can be made, one that does not require as many water changes.

I highly recommend that you consult Walstad’s book called Ecology of the Planted Aquarium. It’s a great read for anyone interested in water gardening.

Submersible water pump, rain bar and pipe

You will need a submersible pump to deliver the water to your grow beds. I recommend using a low circulating water pump. The reason? Goldfish can be stressed by strong currents, and electricity costs are saved by using a lower wattage pump.

The pump should have 3 times the circulation volume (if you have a 100 liter tank, the pump would have a capacity of 300 liters per hour) is a good rule of thumb.

But it could be less than that, as long as the force is strong enough to move the water where it needs to go. You will most likely need to have an elevation of 1 – 1.5 meters high.

The tube will connect to the pump and allow the water to travel to the grow bed, where gravity will return the water to the tank.

I think it is mandatory to use a sponge pre-filter at the pump inlet if the grow bed is used as a filter. Why? Over time, all but the large pebbles (greater than 25mm) will become clogged with debris.

This means that the conversion will be affected in the nitrogen cycle, and the water will begin to «channel» instead of being evenly dispersed for your plants. And that’s not good.

Getting rid of the solids at the start prevents this problem. The sponge only needs to be squeezed or cleaned every week or two.


Some people are very happy with flood and drain facilities, timers, fancy valves, depth of water in the grow bed, etc.

Frankly, those things overwhelm me and I prefer to do things in the simplest way. Also, I like to save money on equipment when possible.) So I prefer to use a rain bar that continuously drips water over the media.

Then you just have to make a series of holes in the bottom of the grow bed to return the water to the tank.

Installation of the culture bed and the culture media Aquaponics

There are many styles of aquaponic setups, but I am going to focus on the most common (and fish-friendly) one: a substantial grow bed typically placed above the aquarium.

If the tank doesn’t have a significant built-in partial lid, you may need to use boards to support the bed so it has a stable resting place.

This is a good kit for a 40 liter (10 gallon) tank:

Grow beds will need special porous media to help the plants retain water and hold them in place. Hydroton Leca is a popular choice for this purpose.

You could also use Seachem Pond Matrix with it or by itself, as it has a very porous surface for room for nitrate-reducing bacteria to grow.

These media options do double duty: they also function as biological filtration media. This means you don’t need to make or buy an additional aquarium filter, your aquaponic grow bed is your filter.

As the water flows over the medium and is exposed to air, it becomes oxygenated and allows the growth of a healthy colony of bacteria that convert ammonia to nitrite and nitrite to nitrate.

water conditioner

The importance of dechlorinating water is well known to most aquarists. But especially in an aquaponics system, many people want to minimize the use of chemicals to grow their all organic produce.

To do this, I recommend ATM Aquarium Vitamin Water Conditioner over the typical chemical-based brands. You stimulate the immune system of your fish and naturally dechlorinate the water.


Unless your grow bed has access to a lot of sunlight or you are only growing plants in low light, you will probably need a special full spectrum grow light for your plants.

This will ensure proper growth and health of the plants. Grow lights make indoor aquaponics possible for those without a sunny room.

Now, it’s not an absolute necessity in some cases, but I also recommend making sure your fish container gets plenty of light as well, which might mean you need to get another light to get it on the fish as well.

LED screens for planted aquariums also allow you to better see the interior of the aquarium to monitor the health of the fish and admire its inhabitants.

Speaking of residents…

Aquarium fish and inhabitants

Goldfish or goldfish are the ideal fish to use in aquaponics. They are hardy, can adapt to a wide range of temperatures, and produce a lot of waste (also known as plant food).

There are two main types of goldfish varieties: slim-bodied and fancy.

If you keep your aquaponic system outside or in a place where it can get cold, you’ll probably want to keep the hardier kind: the slender-bodied goldfish:

  • Common
  • kites
  • shubunkins (and Bristol Shubunkins)
  • Wakins
  • Watoni

These do not require the use of a heater and can overwinter quite well (as long as the water does not freeze solid). That said, in areas with harsher winter climates, your system will still need to be turned off for the winter.

This includes sheltering any plants growing in the tank with the fish if they are not strong enough to survive the cold temperatures.

Fancy ” goldfish are best for indoor setups or very mild climates that don’t have much seasonal fluctuation in temperature. Or, if you have a place to put them inside for the winter.

I also highly recommend adding some goldfish -safe snails to your setup. Snails accelerate the decomposition of waste and are natural cleaners of algae.

Food for goldfish in aquaponic systems

Yes, food plays a very important role in your goldfish’s aquaponic system. The right food will keep your fish alive and thriving and will eventually turn into fish poop, which becomes fertilizer for plants.

Feeding poor quality food to fish can cause problems for the fish and the environment (swim bladder problems and cloudy water to name a few).

And if you’re growing plants to eat like most people, that’s all the more reason to use a good quality feed.

You can find my top picks here: The Best Organic Foods for Aquaponics with Goldfish.


submersible aquarium plants

The large root systems they produce are ideal for those with a gravelly substrate.

The rapid growth of Ceratophyllum demersum “foxtail” is a must start as it helps prevent algae blooms and absorb harmful toxins in the water while your other plants are getting established.

It is also quite indestructible for goldfish.

If you want to keep plants that don’t use a lot of nutrients, grow slowly, or don’t require a substrate, Anubias are a good choice for you.

fox tail. Foxtail is the only exception to that, as it can withstand very cold temperatures.

More information: The best plants for your aquarium

Aquaponic growing plants

What you choose to grow is entirely up to you. The possibilities are almost endless!

Some people opt for garden herbs (especially for smaller-scale systems) or microgreens, while others opt for lettuce and other larger produce. Others use plants that can be used for medicinal purposes.

Different plants have different substrate depths and nutrient requirements, so you’ll need to first research the type of plant you want to grow and its needs.

Also, not all plants like a constant flow of water.

Final thoughts

There is much to learn about aquaponics and goldfish farming, more than this guide could contain. But I hope that what you have read here has been useful to you.

Do you want to share your thoughts? Feel free to drop a line in the comments section below.

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