Why goldfish aquaponics?

Three reasons:

Justify your goldfish obsession to your inquisitive friends and family members.

Grow healthy food right at home.

Reduce or eliminate water changes.

And bonus reason…

Have your pets give back to you for a change.

So what’s involved?

Today I’m going to give you a major rundown on how it works and what you need to get started.

Aquaponics is a massive subject with volumes dedicated to it, so there’s no way I can tell you everything you need to know and I would encourage you to do further research before starting up your system.

That said:

I’ve done my best to download everything I know to you in this guide.

Let’s dive in!

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The Aquaponics Container

Aquaponics containers come in all shapes, sizes and colors.

Some people use horse troughs, barrels or large plastic buckets/tubs.

This 85 gallon Tuff Tank is a popular choice.

Anything 3 gallons and up can be used for aquaponics, but a smaller tank won’t support as much grow media or fish.


You can support 1-2 square feet per 10 gallons of fish water (source).

More gallons = more fish and more plants.

Choosing Your Substrate

Many aquaponics setups either opt for plain ol’ gravel, sand or bare-bottom.

Using some kind of substrate is recommended for several reasons:

  • It provides a home for nitrifying bacteria to convert ammonia into nitrite and nitrite into nitrate (nitrate is then used by the plants)
  • It provides a more natural home for the goldfish, minimizes glare from lights and helps them exercise their natural foraging behavior
  • It allows you to plant several types of aquatic plants that grow large root systems

Sand is an aesthetically pleasing, easy to vacuum option.


Using gravel with goldfish can be a choking risk…

If your pieces are too small.

If using gravel, I recommend using the medium to large smooth gravel (which is more like small pebbles) instead of the pea-size to prevent this.

These large pebbles are about 1/2″ to 3/4″ which is perfect.

They are marketed to turtle keepers (because it is bigger than your typical standard pea gravel) but goldfish owners use them in their aquariums as well.

Gravel alone can be difficult to keep clean and can lead to water quality issues.


I actually recommend doing a Walstad-style substrate with gravel, with a 1″ layer of soil below a 1″ layer of large gravel on top.


According to Walstad:

  • Soil contains bacteria that not only break down nitrite and ammonia – they break down nitrates.  (This is important since waste tends to fall through the cracks in gravel and can get nasty if it isn’t broken down.)
  • It also has Carbonates that stimulate plant growth for both your submerged plants and aquaponic plants.
  • It stabilizes the KH, helping to prevent pH crash
  • The bacteria in soil breaks down fish waste and uneaten food to nutrients that can be used by plants
  • Mineral depletion in the water normally calls for water changes to replenish, but soil continually releases trace elements and minerals into the water over time. This reduces the need for water changes.
  • Soil lasts for years, since the plant and fish waste replenish nutrients they extract from the soil.

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


You will want to plant the tank with this method.

Don’t be afraid of having lots of submerged plants in addition to lots of plants in your grow bed.

They provide shelter for your fish, remove excess nutrients, aerate the substrate with their roots and help with oxygen levels in the water.


It’s usually easier to add more fish and feed more than to struggle with water quality problems from an overstocked system.

Not enough waste is rarely the problem for most systems.


The roots of the plants will prevent toxic anaerobic bacteria pockets from forming in the substrate, as well as take up nutrients created by the breakdown of organic waste.

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

Finally, you do not vacuum the gravel with this method.

That would suck out all your precious dirt and undo your perfect Walstad substrate setup.

Did that register with you?

No gravel vacuuming needed!


Adding the soil/gravel substrate seems to go a long ways towards making a self-sustaining aquarium – one that does not require so many water changes.

Oh, I highly recommend checking out Walstad’s book called Ecology of the Planted Aquarium.

It’s a great read for anyone interested in aquatic gardening.

Submersible Water Pump, Rain Bar & Tubing

You will need a submersible pump to push the water into your grow beds.

I recommend using a low turnover for the water.

The reason?

Goldfish can get stressed by strong currents, and you save electricity costs by using a lower power pump.

The pump should have a turnover greater than or equal to the size of the tank.

3X turnover (if you have a 30 gallon tank, the pump would be rated at 90 gallons per hour) is a good rule of thumb.

But it could be lower than that, just as long as the force is strong enough to move the water where it needs to go.

It most likely needs to have a lift of 3 – 4.5 feet tall.

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

I think it’s mandatory to use a sponge prefilter on the intake of the pump if you are using your grow bed as a filter.


Over time, everything but large pebbles (25mm+) will clog with debris.

This means impaired conversion in the nitrogen cycle, and the water will start “channeling” instead of dispersing evenly for your plants.

Not good!

Getting rid of the solids FIRST prevents this issue.

The sponge just needs to be squeezed out or hosed off every week or two.


Some people get all fancy with flood-and-drain setups, timers, fancy valves, grow bed water depth, etc.

Frankly that stuff overwhelms me and I prefer to do things the simplest way.

(Plus, I like saving money on equipment where possible.)

So I just prefer to use a rain pipe that continuously trickles water over the media.

Then there only needs to be a series of holes drilled in the bottom of the grow bed to return water to the tank.

Setting Up The Aquaponics Grow Bed & Media

There are many styles of aquaponic setups, but I’m going to be focusing on the most common (and well-suited for fish) – a substantial grow bed typically placed over the aquarium.

Sometimes a shelf-style unit is used to support it.

If the tank does not have a significant partial built-in lid like my Seaclear aquarium, you might need to use boards to support the bed so it has a stable resting place.

This is a nice kit for a 10 gallon tank:

Check Price

Grow beds will need special porous media to help the plants retain water and hold them in place.

Hydroton is a popular choice for this purpose.

You could also use Seachem Pond Matrix with it or by itself since it has a very porous surface area for nitrate reduction bacteria growing space.

Get this:

These media options have a dual function – as biological filtration media.

This means you don’t need to make or buy additional filtration – your aquaponics grow bed IS your filter!

As the water flows over the media and is exposed to air, it oxygenates and allows for a healthy colony of bacteria to grow that turn ammonia to nitrite and nitrite to nitrate.

Water Conditioner

The importance of dechlorinating your water is well-understood by most fishkeepers.

But in an aquaponics system especially, many people want to minimize the use of chemicals to grow their produce all organic.

I recommend ATM Aquarium Products Vitamin water conditioner for this instead of the typical chemical-based brands.

After all:

You boost the immune system of your fish AND naturally dechlorinate the water.

If you also want to remove heavy metals as well as chlorine and chloromines – and you want to do it naturally – you may want to try using Auro Liquid Gold instead.


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

This will ensure proper growth and plant health.

Grow lights make indoor aquaponics possible for those without a sun room!

Now, it’s not an absolute must 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 for that as well to position over the fish.

Lighting also allows you to see inside the aquarium better to monitor fish health and admire its inhabitants.

Speaking of inhabitants…

Fish & Aquarium Inhabitants


Goldfish make the IDEAL fish to use for aquaponics.

They are hardy.

They can adapt to a wide range of temperatures.

And they produce lots of waste (aka plant food).

There are two main types of goldfish varieties:

Slim-bodied and fancy.

If you are keeping your aquaponics system outside or in a place where it can get cold, you will probably want to keep the hardier kind – slim-bodied fish.

  • Commons
  • Comets
  • Shubunkins (and Bristol Shubunkins)
  • Wakins
  • Watoni

These don’t require the use of a heater and can overwinter quite well (provided the water doesn’t freeze solid).

That said:

In areas with harsher winter climates, your system will need to be shut down during the winter anyway.

This includes bringing in whatever plants you are growing in the tank with the fish if they aren’t strong enough to survive frigid temperatures.

Fancy goldfish are better 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 speed up the breakdown of waste AND are natural algae cleaners.

Food for Goldfish Aquaponic Systems

Yes, food plays a major role in your goldfish aquaponics setup.

The right food will keep your fish alive and thriving and will eventually turn into fish poop.

Which will turn into plant fertilizer.

Feeding low-quality foods can cause problems for your fish and for your tan (swim bladder problems and cloudy water to name a couple).

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

You can find my top picks here: Best Organic Aquaponic Goldfish Food


Submersible Aquarium Plants

Amazon Swords are fantastic.

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

Fast-growing Hornwort is a must initially in my book, as it helps prevent algae outbreaks and suck up harmful toxins in the water while your other plants are still getting established.

It is also pretty much indestructible to goldfish.

If you want to keep plants that don’t use much nutrients, grow slowly or don’t require a substrate, Anubias is a good option for you.

Most plants will need to be brought inside in the winter or they will not make it to the next year.

Hornwort is pretty much the only exception to that as it can withstand very cold temps.

Aquaponic Growing Plants

What you choose to grow is totally up to you.

The possibilities are almost endless!

Some people opt for garden herbs (especially for smaller scale systems) or microgreens, while others for lettuce and other larger produce.

Still others are using plants that can be used for medicinal purposes.

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

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


How many goldfish should you put in per gallon?

Is there even an easy formula?

It’s actually a bit trickier than one would think, as there are so many different factors at play.

I wrote all about this in another article.

divider3 goldfish bowlFinal Thoughts

There really is so much to learn about aquaponics and goldfish keeping – more than I could contain in this guide.

But I hope what you did read here was useful.

Want to share your thoughts?

Feel free to drop be a line in the comments section below.