Building A Biofilter “or” Trophic Cascades, How Life Creates Life
Ever wonder why natural ponds, lakes, and streams require zero human intervention while human maintained systems are so much work? In short: biology. So let’s take a page from nature and establish a biofilter to maintain a clean, clear, biologically rich fish pond. Chemical free with little extra work. First, let’s look at two ecological principals.
“If there’s a niche, nature will fill it”
“life creates conditions conducive to life”
To understand how these two principals apply, let’s look at the natural cycling process of a typical pond or aquarium. It should be noted that this natural cycling process can take up to a month to establish in any new pond.
Stage 1: Fish You decide to keep fish. Maybe you’re hungry, maybe you’re looking for companionships. In either case you build a pond/aquarium, stock it with fish, and pick up some chow.
Stage 2: Ammonia (NH3) Unfortunately, fish can’t hold it and they end up pooping where they liveWhat’s worse is that fish waste is high in ammonia (a toxic compound created by metabolizing protein) that displaces oxygen, causes organs to shut down, and makes fish susceptible to a host of diseases. Ammonia’s toxic effect is why it’s so effective as a household cleaner. Rub a little ammonia on a countertop and it’ll pretty much kill anything living there. It’s no the kind of stuff you’d like to swim in.
If ammonia is so toxic, how can we get rid of it? The answer: nitrifying bacteria. Some bacteria, as it turns consume ammonia as food. Fortunately, these bacteria are everywhere and exploit ammonia rich resources (if there’s a niche, nature will fill it). Note: you can speed up the process by adding nitrifying bacteria purchased at any fish store (I like Stability).
Stage 3: Nitrite (NO2-) Once ammonia consuming bacteria establish themselves, levels will drop to zero. At this point, bacteria are consuming ammonia as fast as the fish can produce it. In a very real way, fish produce food for the bacteria (life creates conditions conducive to life). Unfortunately, ammonia is converted into nitrite; another (you guessed it) toxic compound. Though as before, new species of bacteria arrive to consume the toxic treat and reducing its presence to zero.
Stage 4: Nitrate (NO3-) After being consumed a second time our toxic waste is finally converted to nitrate. Though benign is makes great plant fertilizer. With ammonia and nitrite levels at zero, there’s no immediate threat to fish, though, if you’ve kept fish, you’ve probably spent hours scraping slimy algae from rocks and walls. Like the nitrifying bacteria before it, these microscopic plants arrived to exploit an opportunity (if there’s a niche, nature will fill it). In a typical pond or aquarium this is usually where we stop…left cleaning, changing water, and/or adding chemicals to keep the pond clear. It doesn’t have to be this way.
Stage 5: Plants If plants (like algae) are almost guaranteed to establish themselves, why not include them intentionally? There’s a lot of ways you could do this. Ornamental aquatic plants are an obvious plan but there’s other interesting options. If you’re fish eat plants, try closing the loop by growing food (duckweed‘s one option). In one system, researchers fed fish the algae their own waste produced. If you eat plants, try your hand at aquaponics. Sky’s the limit!
Stages +6: An interesting way to look at the entire process is to consider that a new organism was added at each stage. In a very real sense, the system moves though a type of succession. Not only did each stage bring new life (if there’s a niche, nature will fill it) but it also brought new opportunities (life creates conditions conducive to life). In a real sense, the fish are a keystone species that enables a whole host of other organisms to flourish. In ecological terms, we call this a trophic cascade. If you remove the fish, the entire system would collapse.
A departure from fish but here’s a fantastic video from George Monbiot (4:34) on how wolves (and the trophic cascades they create) changed the ecology of Yellowstone National Park.
Now. Let’s Build A Biofilter You will need:
- surface area
- water movement
…that’s it. That’s pretty much everything. Nitrifying bacteria grow in colonies that stick to almost any surface. So the more surface area your pond has the more bacteria can colonize it. You can go to aquarium or pond stores to buy expensive materials but any non-toxic surface will do. I like kitchen sponges. How much surface area? The more the merrier. If your pond is natural, there’s a good chance that it already has enough surface area (rocks, sticks, plants, etc). Naturally occurring surface area is one reason why natural systems are self-regulating.
As for water moment, simply make sure that your bacteria are coming into contact with any ammonia and nitrite. Adding a pump to circulate water though a biofilter will ensure adequate contact. As a rule of thumb, I like to circulate my entire pond about once and hour. Though, this depends on a lot of things; how many fish you have, how much you feed them even how warm the water is.
In the system below, I filled a 275 gallon tote with sponges and ribbon (purchased the ribbon at an aquarium store). I then ran two 1200 gallon per hour pumps from the pond into the biofilter. To increase circulation, water was added to the bottom of the tote and allowed to overflow from a pipe at the top.