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The Secret to Gorgeous Plants? Dirty Aquarium Water

So says Metropolitan Farms, and they’ve got pretty good proof—in the form of a 10,000-square-foot farm.

Benjamin Kant (right), founder and CEO of Metropolitan Farms in Humboldt Park   Photos: Jeff Schear

Fish Dew is a pretty coy name for a product that basically amounts to dirty aquarium water.

But Benjamin Kant, founder and CEO of Metropolitan Farms, says it works miracles in the garden—and he’s got loads of beautiful produce to prove it. The Humboldt Park aquaponics farm, which began operations in October, sells homegrown tilapia, greens, and herbs at local farmers markets and supermarkets. Fish Dew, their newest product, debuted when farmers markets opened this spring.

Here’s how it works: Kant and three other full-time workers (plus interns) operate the 10,000-square-foot farm, which consists of tanks of tilapia and a greenhouse. Water circulates between the two systems: The fish create waste, which is converted by naturally occurring bacteria into nitrates and other nutrients. The “nutrient-rich” water (which is what Metro Farms is bottling up and selling as Fish Dew) circulates to the plants, and acts as a fertilizer to help them grow.

In turn, the plants process the nutrients and clean the water so it’s ready to go back to the fish tanks. The closed loop system is popular in the sustainable food movement as a responsible way to raise the fish and the plants.

“I’m known for having a green thumb,” says Kant, who grew up in the Chicago suburbs and got his MBA from University of Illinois at Chicago. “I have a fish tank at home and when I clean it, I pour the water in my houseplants.” It’s a trick that’s well regarded by many gardeners, not least because it puts dirty aquarium water to good use and it’s free.

Of course, Fish Dew is not—it’s going for $8 a gallon—but it is all-natural and non-toxic, and has undergone nutrient testing so you’ll know exactly what comes in the bottle. Gardeners should use it every few days, using regular water in between, and finish the gallon two to four weeks after opening, Kant says. He’s confident people will understand the usefulness of the nutrients and bacteria in the water rather than focusing on the whole “fish waste” bit.

“People aren’t so easily put off things anymore. It’s not a concentrate product, so it’s perfectly safe. You could even drink it and you’d be OK, whereas a lot of chemical-based fertilizers are toxic,” he says. “It’s not, like, sludge.”

Does it work? Kant says the proof is in the pudding, or in his case, the lettuce, basil, mint, and other crops he’s growing in house. I’m inclined to agree: I first tried Metropolitan Farms’ products shortly after they started up, and their greens were just as fresh as any local farm featured on the menus of Chicago’s upscale restaurants.

Back then, the farm only sold whole tilapia directly out of its Chicago Avenue location, and I was asked to bring a bag of ice to transfer the just-caught, still-alive fish. Now Metro Farms’ offerings are fileted and pre-packaged, if you’re so inclined, but the whole fish was so fresh that I happily spent half an evening scaling and gutting the sucker and steaming it whole.

The farm will soon start selling homemade pesto and is expanding its crops to include mustard greens, Asian greens, watercress, and chard. Diversification is Metro Farms’ way of “trying to find our place in the world,” says Kant, who learned to raise fish from his grandfather as a child. “I have these memories of working in the garden, picking beans to bring in to dinner. To make a career out of it seemed like such a fantastic opportunity.”


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