Why Oil and Fish Don't Mix

By Bill Moore

Posted: 30 Dec 2011

I have a new hobby. Actually, it's my only hobby. I am into aquaponics. Heard of it? It is a bio-synergistic system that melds hydroponics and aquaculture. Hydroponics, of course, is the growing of plants in essentially a soil-less medium. Lots of the tomatoes you find in the stores in the depth of winter are grown hydroponically. In Montreal, Lufa Farms grows a wide array of vegetables and herbs, hydroponically in a greenhouse atop a warehouse in the middle of town.

Aquaculture is the raising of marine life in captivity: basically aquatic 'farms', if you will. Some operate out in open water, typically shallow coastal pens. Some are land-locked ponds and fish runs depending on the species being raised: prawns, catfish, trout, salmon.

Both have a common problem: effluent pollution. Hydroponics requires the application of liquid nutrients -- fertilizers -- since the medium, itself, is for hygienic reasons, essentially sterile. These must be replenished periodically and eventually replaced: i.e. dumped into the environment. Aquaculture has a similar problem. Marine life produce their own biological waste and since they are raised in very confined spaces, the accumulated effluents become toxic to the fish and environment around it. At sea, this gets dispersed by the tides. In land-based operations, it has be continually filtered and/or disposed of and fresh water added.

It turns out that if you carefully combine the two systems: the plants and the fish, they actually complement each other. The fish provide most of the nutrients that the plants need, while the roots of the plants and the bacteria colonies they harbor filter and purify the water for the fish.

So, how "into" aquaponics am I? Somewhere a bit over $1,000, if we're talking financially. That bought me two 50 gallon Rubbermaid Ag water tanks; one 100 gallon Ag water tank, also Rubbermaid; a couple dozen feet of one and two inch PVC plumbing pipe, couplers, ball valves, etc. It also bought three bags of Hydroton, an expanded clay pebble imported from Germany, and a pair of salvaged commercial metal halide lights I found locally on Craig's List. It also bought me a small, submersible electric pump; and it is that pump to which I now draw your attention.

As I was spec-ing out my CHOP2 system, developed by Murray Hallam, one of the leading aquaponics 'gurus' based in Australia, I spent a fair amount of time at Home Depot and Lowes, as well as the local Menard's outlet. I wanted to find a local source for my pump, if possible. Of course, what you find are your typical basement sump pumps. As I carefully looked over each model, I came to the sobering realization that none of them could or should be used in an aquaponic system.

Why?

They all use oil for lubrication; oil that can leak into the water and contaminate both the grow bed and pollute the fish tank.

A CHOP2 set up works this way. Water from the sump tank -- in my system, that's one of the 50 gallon Ag tanks -- is pumped both directly to the second 50 gallon Ag tank directly above it, as well as into the 100 gallon fish tank next to it. The 50 gallon 'grow bed' is filled with a combination of red lava rock along the bottom two inches, and Hydroton above that to a depth of some 8 inches. The Hydroton is the sterile, pH neutral medium in which you grown your crops. In our case at the moment we have Swiss chard and radishes. Even though I only officially started the system in early November, we've already been harvesting the chard, which successfully transplanted, much to my surprise and delight, from the outdoor garden after throughly washing off all dirt from the roots.

The water level in the 50 gallon (53 inch x 32 inch X 12 inch) grow bed is controlled by an ingenious bell siphon system that still amazes me to this day. You can find video instructions on how to build it on YouTube. It works by automatically creating a siphoning effect that drains all but the last two inches or so of water from the grow bed about six times an hour. This tidal effect, of sorts, sucks air down into the grow bed, helping the bacteria colonies thrive. Those colonies convert the ammonia produced by the fish -- it is a byproduct of their bodily waste and gills -- first to nitrate and then to nitrite, which the plants take up. In the process, the water is purified. As the water literally gushes down to the sump tank once every ten minutes, it is oxygenated. The little oil-less pump then recirculates it back to both the fish tank and the grow bed. The water in the fish tank drains by gravity back into the sump, at which point the process begins all over again. It is fascinating to watch, especially since adding the Comet goldfish once the bio-filtering bacteria colonies got established.

As I was researching all this through the summer and into the fall, when it came to selecting the pump, everyone cautioned, do not, under any circumstances, use a commercial sump pump that uses oil for lubrication. Even the smallest amount will contaminate the entire miniature eco-system you are attempting to cultivate. So, I walked out of all three stores and found what I needed online: a small submersible pump that uses magnetic bearings. This is the type you'd use in a Koi pond.

I decided to write about this -- and share my new hobby of growing fresh food and fish in my basement this winter -- because of an article in the Los Angeles Times that reports on the phenomenon of phototoxicity. The National Oceanographic and Atmospheric Administration and UC Davis' Bodega Marine Laboratory studied the effects of 2007 Cusco Busan oil spill in San Francisco Bay on marine life, and specifically on Pacific herring, which spawn in the bay. They found that when the herring embryos absorbed oil from the spill and then were exposed to UV rays from the sun, they quite literally disintegrated. Writes the Times, this phototoxicity "has not previously been taken into account when talking about oil spills."

“This phenomenon had been observed in the laboratory, but had never been observed in the field, and there were even some skeptics out there wondering if this was just a phenomenon that people would see under lab conditions,” said Gary Cherr, director of the marine lab and professor of environmental toxicology.

“One of the real take-home messages from our study was: yes, in fact, it definitely happens in the real world.”

The Cusco Busan oil tanker spilled an estimated 54,000 gallons of bunker fuel in the Bay; the Deepwater Horizon blowout in 2010 was magnitudes above that level, and although much of that oil remained low in the water column, what did rise to the surface, "could have produced phototoxic effects that are still unknown and unstudied, " concludes the LA Times.

My miniature ecosystem is maybe 130 gallons of water, which I carefully monitor for pH and temperature daily -- that was another $90 for a digital meter -- and for ammonia, nitrate and nitrates on a weekly basis. The last thing I want happening is for oil, even in the tiniest amounts, to leak into the system and poison my seven goldfish -- to be supplemented with tilapia eventually -- and contaminate the grow beds.

Meanwhile, have you seen the BP-funded television commercials promoting tourism on the Gulf Coast, saying everything is fine, "Come on down."

Wow. That's chutzpah!

Firstwave Aquaponics test system

You can follow my adventures into Aquaponics on Facebook.com/firstwaveaquaponics.

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