ATP Podcast #59: Aquaponics, and Growing Outdoor Plants Indoors

Let's talk about aquaponics, the raising of fish and plants in a symbiotic relationship.

The primary thing that fish really need is clean water. This is a challenge because fish constantly produce ammonia which is converted by bacteria in the tank into nitrites. Other bacteria then come along and convert the nitrites into nitrates. Over time the water becomes saturated with these nitrates to the point that it becomes toxic to fish.

Now, the primary thing that plants need is certain nutrients. One of the most important nutrient of them all is nitrogen, which plants use to produce the chlorophyll which makes their leaves green in color. The more green leafiness a plant has, the higher its nitrogen requirements are.

Well, put these together and you can see where I'm going with this. The nitrates produced in your fish tank can be used directly as a nitrogen fertilizer for plants. The plants use the nitrates as fertilizer, and return the clean water back to the tank where the fish can thrive. This is the fundamental principle behind aquaponics.

The most common setup is one where there is a growing bed filled with gravel (no soil) where water can be pumped from the tank of fish into the gravel bed where we grow plants. The plants absorb and use the nitrates in the water, and once the water returns to the tank, it has been filtered and is free of nitrates. The cycle continues indefinitely. Fish manure is also a valuable fertilizer, containing many other valuable nutrients in addition to the nitrogen.

There are many complicated setups to achieve this, but for newbies to aquaponics, I highly recommend using the IBC tote system. You take a 250 gallon IBC tote, cut off the top 12 inches, turn it over, and you now have the big tank below for the fish, and a nice container up top for the gravel. Plumbing them together is a bit beyond the scope of this introductory article.

Oxygen in the water is critical to ensure success. Use aquarium bubblers in the tank, and the pump you use to fill the gravel bed should have a tee installed so that some water falls back into the tank. This mixing and falling action will be enough to give the water the oxygen it needs.

Dead roots from plants, along with fish manure, will slowly build up and gum up your gravel. Consider keeping worms in your gravel grow bed to help the excess matter get eaten up and returned to the water in soluble form.

pH is important to track. Limestone will constantly raise the pH. Maintain pH around 7.2 and add ground limestone to increase the pH. pH tends to continue to drop because the fish and plants have an acidifying effect. If you use limestone based gravel for your grow bed, you will be constantly fighting a losing pH battle. Choose inert gravel. To test the gravel, drop a piece of it in a bowl of vinegar. If it sizzles, don't use it!

The initial startup of your fish tank is important. Once you add fish to a new tank, the bacteria needed for the ammonia conversion are not yet established. This process can take a month or longer! Start with fish you're willing to lose. If you have an aquarium in your house, you can speed up the process by adding some of the aquarium water into your new aquaponics tank. This will inoculate the water with the bacteria needed and dramatically speed up the process.

Catfish, large mouth bass, and tilapia are commonly raised fish. Bluegills and crappy will work in a pinch. If you're only after the plants and don't care to grow fish for eating, you can use koi, carp, minnows and even goldfish.

The aquaponics system must be temperature controlled and shouldn't be allowed to get extremely hot or cold. In a greenhouse is the best environment to practice aquaponics. An added benefit here is that you can use the water from the tank to water your other plants! The specific temperature of your tank will be determine by the species of fish you choose to grow, so be sure to research that. Some fish are more tolerant of wild temperature swings than others.

Finally, watch out for power outages. If the pumps and aeration systems stop, even for a time as brief as an hour, your fish will die. When you get serious about aquaponics, you will want to add an "off the grid" solution for your pumps. The most common setup is a 12 volt battery, hooked up to a charger to the grid on one side, and an inverter on the other side. The pumps are then operated off the inverter.