Friendly Aquaponics

Cleaning Your System; Fish Tank And Troughs

Our systems collect “solids” until they are 2-3 inches deep in all eight of the 80-foot long troughs; we’ve coined a technical term for this: crud. It comes from potting mix that gets pushed out of the slit pots by the expanding action of the plant’s roots when they grow; more potting mix just falls out when planting and transferring pots, and everything living in the trough water dies sooner or later. Roots fall off plants in the water, mosquito fish die and sink to the bottom, and there’s lots of “organic stuff” coming in with the new water from the fish tank which settles to the bottom of the troughs. All this results in a smooth, sweet layer of silky mud (with some gritty coir mixed in). When you bring a handful to the surface of the trough and smell it, the smell is similar to that of the leaf mold layer on a forest floor underneath the trees; it’s rather earthy and sweet-smelling.

(Below) A cute baby. What? Did you really expect a photo of aquaponic crud?

When the system is managed so that there is not too much fish poop, nor too much other decaying organic material in it, then the crud in the bottoms of your troughs will smell sweet, like the leaf mold on the forest floor. Although we haven’t analyzed it (we’d love to have the funds for a study on “aquaponic crud”!), we feel it functions kind of like a nutrient reservoir, keeping micronutrients available to the plants without requiring monitoring or careful nutrient supplementation as is needed in hydroponics systems.

What the heck are micronutrients? There are 17 elements considered essential for plant growth. Three of them—carbon, hydrogen and oxygen—are supplied by the air and water around us and are generally not thought of as fertilizers. Of the remaining 14 elements, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are technically considered macronutrients (“macro” is bigger than “micro”). Iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel are recognized as micronutrients. Often all 14 are referred to as micronutrients.

This crud freaks people out! They want to “clean it up”, “control it”, and vacuum it out of existence! However, we’ve never seen this crud cause a problem, as long as your system is managed carefully (we’ll explain what that means next), even when it builds up to almost 4 inches deep in the long troughs in our commercial systems.

You don’t have to remove or “clean” the crud!

The crud is part of a healthy system! It’s just like the mud in the bottom of a lake or in a pool in a mountain stream; and you wouldn’t even think about cleaning that stuff up, would you? You know it’s a natural part of the ecosystem of the stream, and is full of bacteria, little critters, minerals and nutrients. Well, the crud in the bottom of an aquaponics trough is the same; and in our eight years of experience, we’ve only found it to cause problems in one specific situation: when there’s too much decaying organic material (ie fish poop) coming out of the fish tank and going into the troughs. Then, it does smell bad, and emits stinky bubbles when you put your hand down into it.

Here’s why: normally, the bacteria in the crud in the bottom of your troughs turn the fish poop and other decaying organic material in your troughs (dead mosquito fish, dead plant roots, etc) into ammonia, then the nitrifiers in the system turn it into nitrites and nitrates, which fertilize your plants. But, if the bacteria that turn decaying organic material into ammonia get overwhelmed by too much fish poop, you start to see other biological processes occurring, such as the one that turns some of it into hydrogen sulfide (hydrogen sulfide gives off the “rotten egg” smell). When this starts to happen, the stuff in the bottoms of your troughs will smell more like an outhouse than leaf mold from the forest floor.

If this happens to your system, it is easy to fix. We overloaded our troughs once on purpose to see what would happen during a 3-month experiment. When the experiment was over; the plants were suffering and not growing well at all; we dumped the troughs, including their crud (onto the banana trees) and refilled. Everything in the system was within normal operating limits 3 days later, and the new plants we transplanted grew just great! So even if you forget to pay attention, and this does happen to your system, it’s no big deal; it’s this easy to get back on track!

The stuff in the troughs is a natural part of system operation, and you really don’t need to do anything about it until it gets 4 inches deep in all your troughs (this usually takes from 4 to 6 years), or until it starts smelling bad and emitting hydrogen sulfide bubbles when disturbed as we just noted. Usually we get root aphids or some other nasty critter or disease every three or four years, and we take that opportunity to dump the entire contents of the trough on the bananas; letting the trough self-sterilize in the sun for a couple of days before refilling it. It’s a minimal interruption in the productivity of your system to have one trough out of action like this, and better than the alternative.