How I transformed my freshwater aquarium into an aquaponics garden for year-round organic produce (and stopped doing water changes).

To be honest, I never really considered myself a “fish guy”. I always had pets growing up, but fish seemed so… passive.

How I became a fish guy is a kind of a funny story.

It all started with my daughter, who decided she wanted a pet fish. So like any good father would, I took her to the local PetSmart and she picked out a very cool Black Ghost Knifefish. I bought myself a very stylish looking 10 gallon aquarium for the little guy’s new residence, some fish food, and brought it back home.

Within 24 hrs, the fish was dead. So I took it back to PetSmart, certainly it wasn’t I who was responsible the fish must have been sick! They gladly allowed me to return the fish per their two-week life policy and we started again.

This happened at least 6 more times over the course of the next two weeks. I couldn’t keep a fish alive! My constant fish genocide prompted me to learn what I was doing wrong (turns out I had no idea what an aquarium nitrogen cycle is), and by the time I was finished I realized I really liked keeping aquariums! Now I have three tanks in my house: a ~150 gallon Freshwater tank (I have among other things, a turtle and two large beautiful Black Ghost Knifefish), a ~150 gallon saltwater tank, and a ~3,000 gallon Koi pond outside!

In this article we aren’t going to focus on my aquariums themselves, but instead we’re going to focus on all that waste the freshwater fish produce. If you read up on the nitrogen cycle, you will learn the reason you have to regularly do a “water change” (take out water, add new fresh water) in a fish tank is because over time the waste produced causes a build-up of nitrates. In high levels, nitrates are very bad and even lethal to your aquatic friends. Being a generally lazy person, I quickly found it very challenging to keep up on this important task with any sort of regular schedule so I started looking into ways to simplify my life. Not to mention how much water you literally pour down the drain!

One very cool answer is aquaponics. Aquaponics is a plant growing technique similar to hydroponics, which is basically growing plants in a medium other than dirt with water. The cool thing is this: Where a Hydroponics system requires you to add nutrients to the water to feed your plants (basically fertilizer), an aquaponics system uses all the nitrates produced by your fish as natural fertilizer! What a perfect solution for my laziness – I can stop doing water changes and let plants do the work for me, all the while saving (a bit) of water and always having home-grown produce on hand! Moreover, if you were so inclined, instead of keeping decorative fish like I do, you could grow tilapia and not only grow veggies but fish to eat as well!

So how does this work exactly? There are lots of different configurations, but basically the concept itself is very simple: You start with fish in one place living their lives and producing waste, then you take water from that tank and run it through one or more growing beds where your plants can absorb the nutrients, then put the water back into the tank with the fish.

For my setup, my freshwater tank is a 90 gallon overflow tank. Overflow tanks have been around forever and typically are used in saltwater tank setups. The idea is simple and requires two separate tanks. First is your “display tank” where all your fish live, and then a second tank called a sump where all of the equipment to keep the fish healthy is located (heaters, filters, etc). A sump tank always needs to be lower than your display tank (to allow water to drain properly from the display tank), and typically is hidden in the cabinet of your fish tank stand. This setup generally is used just to make the tank look prettier since you don’t need to have it cluttered with ugly equipment — but it also makes for a great aquaponics setup. Basically what happens is you have a water pump pumping the water from the sump into the display tank, and as the display tank tank fills up it reaches it’s maximum capacity and then water drains out of it and back down into the sump. For an aquaponics setup we add another step — let the water flow into grow beds from the display tank, then into the sump to be pumped back up.

In my case, I have something a little more ambitious as my sump isn’t under my display tank but actually in my basement. Exact same principal, but doing it this way allowed me to keep the sump tanks for both my saltwater and freshwater aquariums in one corner of my basement where I could manage everything (sort of an aquarium control room). Here’s a rough idea of what my set up looks like:

Sounds pretty simple right? Mind you there is obviously a lot of PVC plumbing to create, but conceptually an overflow/sump setup is pretty straightforward. Unfortunately however there are a few details about adding grow beds that I’ve left out that we need to talk about a bit to create our aquaponics garden!

If you spend some time reading about hydroponics systems, you’ll learn it’s not quite as straightforward as sticking a plant in some nutrient-rich water and letting it grow. The water has to be in a near-constant state of movement for starters, and believe it or not the roots actually need to be exposed to the air as well (otherwise you get root-rot and your plants die). There are a number of methods for implementing this, but the one I like is called an ebb and flow (sometimes called flood/drain) setup and that’s what I’ll be discussing here.

In an ebb and flow hydroponics/aquaponics setup your grow beds need to (appropriately) fill up completely with water, then drain completely and start again. There are plenty of ways to implement this, with the most obvious one is some sort of complicated series of pumps moving water around. That’s a really bad idea though, because water pumps use a lot of electricity and if the wrong one stopped working you could end up just pumping water onto your floor! For our system we want to make sure a pump failure doesn’t cause a flood, and simplify our setup as much as possible.

The answer is to use a very clever plumbing contraption known as a Bell Siphon which is designed to do exactly what we need in our grow beds. A Bell Siphon is designed to create an automatic siphon of water once the water reaches a certain height, and to do so in such a way that the rate at which the water drains out through the siphon is considerably faster than the rate water is filling the grow bed. As the siphon drains the water, holes at the bottom of it cause the siphon to break suction and the whole process starts again.

Bell Siphons can be a bit tricky to get right, but once you have them working they are extremely effective and I use them in all four of my grow beds. From the grow bed, through the bell siphon, the water makes it’s way into my sump tank where it is heated (to keep the fish happy) and then pumped back up into the display tank to start again!

In my next article, I will dive into the details of the actual construction of my aquaponic grow beds. Stay tuned!