I recently decided to try my hand at aquaponics! I’ve been doing regular hydroponics for a little over 10 years, both as a hobby and a job. Hydroponics is the process of growing plants without the use of soil. Instead, you use an inert growing medium and special fertilizers made for hydroponic growth. Another hobby of mine over the last 7 years or so had been keeping tropical fish aquariums. I have a marine (salt water) tank at home and two fresh water tanks at my retail gardening store. So I thought to myself, why not combine the two hobbies? I started reading Aquaponic Gardening by Sylvia Bernstein, and it instantly hooked me. Now, when I get something in my head that I really want to do, I want it done right now. So, an hour later I had a basic DIY aquaponic set up built onto my existing aquarium.
Aquaponics is a type of hydroponic growing in which the fertlizer used is actually generated by the fish themselves with a little help from some beneficial bacteria. There is no need for additional fertilizer. Likewise, the plants then filter out the water by sucking the nutrients out of it and thus negating the need for weekly water changes on your fish tank — a perfect symbiotic relationship.
There are two different types of aquaponics. The type I did is a smaller scale using “pet” fish, but you can also do a larger scale operation in which you not only get fresh produce from your garden but also fresh fish for your dinner table. I was obviously not planning on eating my fish, I’ve grown quite attached to them and yes, they all have names.
Having an existing aquarium was a huge time saver. The tank had been set up in the store for 5 or 6 years at least, so it was well established. A fish tank needs to be “cycled” through a series of biological events in order to be able to sustain life. Fish waste produces ammonia which is toxic to fish, so in an enclosed environment such as a tank, the ammonia levels can rise quickly and endanger the fish. The tank needs time to build up beneficial bacteria which will break the ammonia down into nitrite. Nitrite, however, is actually more toxic to fish than ammonia. Fortunately, a second type of bacteria will develop that will convert the nitrite into nitrate which is not nearly as harmful and is also a fantastic fertilizer. See where I’m going here? These bacteria will develop naturally, it will just take time. Now in a normal fish-only aquarium you would need to remove the nitrate manually by doing weekly water changes. When you add plants into the mix they will take the nitrate out for you and use it to grow.
I’ll walk you through what I set up here at the store. I decided that a basic ebb and flow system would be the easiest. Ebb and flow just means that the grow tray fills up with water and then drains back down into a reservoir, which in this case is the fish tank. I used a white grow tray that’s used for hydroponics (its dimensions are 36-by-8-by-4 inches), a fill and drain kit, which is just a couple of fittings that are used to attach a water pump to, and a 160-gallon-per-hour water pump.
I drilled two 1-1/4-inch holes side-by-side in the grow tray with a hole saw and attached the fill and drain fittings. The taller of the two fittings is the overflow, which keeps the water from overflowing the tray, and the shorter is the fill. I used a length of 1/2-inch vinyl tubing to attach the pump to the fill fitting and placed the pump in the tank. Now, I was lucky in the fact that there was a large plant shelf right next to the tank already, so I just pulled it closer and put the grow tray on it. I had to raise the tray with a cinder block to get it higher than the top of the tank and on a slight angle so the water would flow back down into the tank via gravity. You could just as easily place the tray directly on top of the tank.
I had already had some basil seedlings ready to go that I had started weeks before in rockwool (an inert medium) so since I wanted instant results, I went with basil — Sunleaves Rocks was my medium of choice.
I filled the bottom of the tray, placed my basil seedlings in, spaced about 8 inches apart, and filled in the rest of the tray with the rocks. I plugged the pump into a standard timer and set it to flood the tray for 15 minutes every hour. Then I grabbed some red worms out of our worm composting bin, about a handful, and added them to the grow tray. The purpose for this was that the worms will eat any solid fish waste that gets pumped up into the tray and convert it to worm castings (another fabulous fertilizer). I hung a high-output fluorescent light over the tray and voila, I was done!
In order to keep the fish, plants and bacteria happy the pH of the water must be kept between 6.8 and 7.0. If it gets much lower than that, the bacteria will suffer and slow the conversion of ammonia and nitrite. Much above and the plants won’t be able to absorb the nutrients needed to develop and grow. PH regulator solutions made for hydroponics should do the trick. Just remember not to adjust the PH more than .2 degrees in a 24 hour period or the fish will suffer.