Part 3: Lessons We Learned From Our First Year With Aquaponics

By Scott Beuerlein, Horticulturist

Sustainability Intern Mary Sticklen teaches guests about aquaponics during the 1:30pm Keeper Chat.

Fish

After extensive conversations with the genius engineers who helped me start the system, and a couple of really smart and friendly experts at Jones Fish Hatchery, I chose to go with bluegill and catfish (which, by the way, were donated by Jones Fish Hatchery). There was wild enthusiasm around the Zoo for tilapia, but I had worries using a tropical fish in a system that would not only be a start up with the oscillating fluctuations in water quality that goes with that, but would also experience significant daily changes in water temperature during winter. Our system is heated—kept at a minimum temperature in winter of around 60F, but on sunny days the greenhouse can zoom up to 80F, which is the point where it vents. Water temperature would follow, and I was not sure tilapia could handle that. So I chose catfish and bluegill, despite everybody’s wishes, and endured weeks of abuse and ridicule until another dude made an even worse decision.

The fact is the bluegill and catfish did well, and I still feel it was a good decision for that time. Early on, we did experience a wild ride of water quality before the bacteria stabilized and before the plants grew on enough to achieve adequate balance with the fish. More importantly, our water hardness is astronomical and that’s not something we have much control over. Bluegill and catfish are unfazed.  Even more impressive, due to a learning curve (read: “series of blunders”) on the water return system (described later), the system virtually drained itself of water on several occasions. Needless to say, the only choice upon finding nearly empty tanks was to fill with tap water.  Of course we added this water at the far end of the system, allowing it to pass through both our gravel and raft tanks which brought it closer to temperature and possibly helped to release some of the chlorine, but this was far from ideal. Nevertheless, we never lost a fish due to this, which is a real testament to the toughness of these species of fish.

In recent weeks, however, we have had a couple of issues with the catfish, in part because they are a scale-less fish.  After consulting our Curator of Aquaculture and Reptiles, Jeff Mitchell, my worries about tilapia have been allayed, and we are considering a gradual replacement of the catfish with them.

We have lost fish. Early on, we had a few jumpers. Since this occurred almost entirely when water quality had not yet stabilized, there’s been some speculation that maybe this was the cause. Maybe it was because I was singing too many Nick Cave songs while working in the greenhouse. Who knows?  Things have gotten much better, and we seldom lose any fish.

As for harvesting fish, we haven’t done that, although the decision looms. Yes, I have in fact named all the fish and we’ve had some good times together. This probably wasn’t very smart. Chef never did bond with any of them, and he sees the fish only as the delicious fillets they might one day become. We’ll see what happens. A year ago we started with 6” or smaller fingerlings. The catfish now appear to be 3-5 pounders.  The bluegills are still fairly small and not yet what a fisherman would call a “keeper.”

Plants

Our best successes have been tomatoes, basil, bok choi, beets, chard, and chives, with some basil, chard, and tomato plants living for nearly a year. We had tomatoes producing in all but the darkest few weeks of a very cold and gray winter. Disappointments have been peppers and lettuces. The difference between success and failure seems to be the ability to grow fast and strong. Aggressive growers seem to skirt past that vulnerable seedling stage where aphids, snails, and damping off take them before their time. In just the summer months last season, we harvested over 30 pounds of basil.

Freshly harvested basil, ready for the cafe kitchens!

Germination is almost instant in the wet, warm environment, but there’s a slow, lagging period until the seedlings finally reach a decent size. Once there, plants grow very vigorously, and respond to repeated harvests with very strong bursts of re-growth.  We’ve been trying to boost plants through the seedling stage with foliar fertilization, using fish emulsion and seaweed extract.

It is interesting that in the Fall, when daylight hours noticeably decreased, most of the plants responded by a marked decrease in growth, and no amount of fertilizing or other means seems to make any difference. It is just the plants natural response to diminishing daylight. It appears temperature is not a factor, because as the day length increased in early Spring, which wasn’t any warmer, the plants responded by putting on strong new growth.

Pests and Diseases

Overall, we’ve experienced remarkably few issues with plant or fish health in regards to pests or diseases. Our only two issues are snails and aphids. I don’t know how snails showed up, but they appear to be here to stay. There’s really no control, except to periodically lift the foam rafts and hose the little devils off into the gravel. This seems to keep their numbers low enough that the plants can grow past their predation on roots. The problem seems much less in the gravel and hydroton beds than in the raft beds.

Aphids are interesting. Their numbers ballooned as we went into the Winter months, and it was a challenge to keep them controlled with organic treatments of Spinosad and insecticidal soap. Aphids alone, I believe, prevented us from growing lettuce. At one point this Spring, all on their own, Lady Beetles (and their voracious larvae) showed up and had a noticeable effect on aphid numbers.  But, just as they mysteriously arrived, they mysteriously disappeared, but so did the aphids. Maybe it was the heat?

My philosophy with the aquaponics greenhouse is that if a crop is difficult, we’ll replace it with one that isn’t. We don’t have the time to make pest control a lifestyle. Becoming an expert on treatments isn’t on my bucket list, and we certainly aren’t going to introduce chemicals into an ecosystem whose whole success hinges on the fine balance of fish, bacteria, and plants. Nope, that’s a high wire act that doesn’t need morel variables.

Fertilizers

As mentioned before, foliar sprays of fish emulsion and seaweed extract (iron added) provide a wonderful occasional boost, especially to young or heavily producing plants. For some reason, iron is commonly low in aquaponic systems, as are calcium and magnesium. Because of this, once in a blue moon I add a dollop of seaweed extract (with iron) and a product called CalMag to the water. Call me crazy, but I can almost witness plants greening up and growing after application.

Cleaning

We don’t clean as often as you would think. This is as intentional as it is convenient. Aquaponics depend on healthy, functioning bacteria. Aggressive cleaning is detrimental to bacteria. So, we’re rather lackadaisical about scheduling heavy cleaning, especially of the bio-reactors, and we’re not very thorough about it when we finally get around to it. I learned this lesson from installing and maintaining garden ponds, and I learned it well. Give bacteria their space, and they’ll play nice.

Water Quality

Our water is hard, and will stay hard. Fact of life for city dwellers in the Midwest. The pH creeps down constantly, and I need to keep an eye on that. Otherwise, the system is remarkably stable. An interesting point about pH. You’ll remember that our system is split into two sides. The left has one tank filled with expensive clay balls called Hydroton, which overflows into a foam raft tank. The right has one tank filled with practically free round limestone gravel. It also spills into a foam raft tank. The pH on the Hydroton side was always threatening to fall below safe levels, requiring me to add things to try to bring it back up. But the gravel side remained remarkably stable. If you think about it, this makes perfect sense, because what’s better than lime to moderate acidity? We have half a ton of limestone gravel filtering every ounce of water as often as it passes through the system. One day it finally occurred to me, put a layer of limestone gravel on the floor of the Hydroton’s side raft bed, and see what happens. I did, and it has worked. The pH remains a little low, but not so low that I have to worry about it as much as I did.

Grow bed filled with clay balls called Hydroton.

When we began, I obsessed over water quality, testing constantly. Gradually, came to rely on the system and lost precious little sleep. More recently, we had a few problems with the catfish and Jeff Mitchell, our Curator of Aquaculture and Reptile, thought these were attributable to some water quality issues. We backed off on our feeding regimen some, which has lowered nitrate and nitrite levels, and we’ve been more aggressive about changing out water. Our problems have abated. Moral of the story: don’t get too complacent on water quality. You should lose a little sleep over it from time to time.

Turface and Rockwool

Rockwool is a heat expanded rock product that looks and feels very much like fiberglass insulation. It’s not cheap and I really don’t like the stuff. I have to use it on the raft tanks, because it prevents the plants from falling through the holes and into the water. Initially, I was told to use it on the gravel and hydroton beds too, which I dutifully did. But soon I began to wonder if I could just plant seed in those beds directly. I tried, and it mostly didn’t work. Much of the seed fell down through the crevices into the water. But I knew from starting rare plants from seed at home that Turface is a very useful product in media mixes. It’s a calcined clay product that looks like kitty litter. It is often used on baseball infields to dry up puddles or raise low spots. It has an astronomical amount of surface area, holds a lot of water, has an enormously high cation exchange (ability to hold nutrients), and I knew a layer of it on top of the gravel and hydroton would keep the seeds where they could germinate. It worked just as I suspected, and I haven’t looked back since. No expensive, gross rockwool in the gravel and hydroton beds, seeds are sewn direct.

Basil planted in Rockwool, ready to be placed in the floating rafts.

Take Home Message

How sustainable is our system, and how sustainable is it for the average guy to do at home? These were questions we wanted to answer when we started the system. For us?  We started with a nice but fairly expensive greenhouse with a heating system, which means heavy costs up front and not incidental operating costs. Harvests exceed operational expenses, I’m sure of this, but how many years of operation will it take to recoup the initial capital costs? That’s a question for the genius engineers, I’m pleased to say, but certainly it would take time, and also the continued commitment of someone who is fairly passionate about the system. If our system were larger, enabling greater harvests, I believe that the relative harvest to costs ratio would wind up in the favor of aquaponics. But, again, over time. Less time, but still time. This is one reason why this system is so intriguing for urban agriculture.

Interestingly, I think for the homeowner on a budget who puts minimal capital into the system in the early stages (subbing a poly tunnel for a glass greenhouse, for instance), the prospects of economically sustainable success are improved. For one, the system can be opened in the summer to allow naturally occurring insect populations to limit pests, but also because you wouldn’t be heating the system in the winter. Yes, this brings production to a crawl for a few months, and you would also have to face the issue of getting the plant/bacteria/fish/water quality balance steadied every Spring, but you would have saved a ton of start up costs. There is still much to learn and improvements to make, which is to be expected from something so new.

Please come visit our greenhouse, which is located near the Base Camp Cafe. Weekdays during the summer months, we have a keeper encounter there every afternoon at 1:30PM. You’re also welcome to schedule a tour with us by appointment. Email Fia at gogreen@cincinnatizoo.org or myself, at scott.beuerlein@cincinnatizoo.org.

Contributors: April Pitman, Wendy Rice, and Jenna Wingate

Mandy Pritchard works as a keeper at World of the Insect, also called the Insectarium. Mandy has a solid entomology background and she is very knowledgeable of the biology and taxonomy of a variety of different species of insects. As a keeper, Mandy is in charge of maintaining and breeding 15 species. Most of her species require fresh plant cuttings, so you will see her out in the park every day (rain, shine or snow) looking for the best plants for her cultures.

According to her colleagues, Mandy is an awesome coworker. She helps train volunteers and new hires, and whenever her coworkers go to her with questions, she is always open and willing to help. Mandy is very easy to get along with and is one of the reasons the Insectarium is such a team-oriented and cohesive department.

Mandy Pritchard introducing American Burying Beetles

Additionally, Mandy is an awesome representation of the zookeeping profession because of her passion for conservation. She goes above and beyond her job as a keeper. Currently, she is in charge of the American Burying Beetle reintroduction program at the Zoo. She successfully collaborates with other agencies outside the Zoo (Ohio Fish and Wildlife, Fernald Preserve, and more) to work towards a lasting conservation solution. The program itself is requires much diligence and hard work. Mandy is in charge of organizing dates for the release, helping to staff the release, raising the beetles, setting traps to survey the area before and after the release, and much more.

One of the most important things keepers do is educate the public on conservation and Mandy does a great job of that. Sharing her passion with the public comes naturally to Mandy. She just recently gave a talk at the Fernald Preserve (where the beetles are released) to help educate the public on the importance of this species. It is not the easiest thing to show people why this beetle should be saved. Most people just see it as another bug! But Mandy does a great job of enlightening everyone, keeping the audience interested and even getting a few laughs, too! Mandy has the ability to make people care about something they never thought they would. Keep it up, Mandy!

Part 2: How Aquaponics Works In Spite of Everything

by Scott Beuerlein, Horticulturist

How It Works

So before we go into the “lessons learned,” which will be our final installment, here is a quick briefing on how aquaponics works. Aquaponics is a closed loop agricultural system in which fish are raised in a tank. Water from the fish tank is continuously pumped up to a bio-reactor, which is a fancy word for a small filtration system that mainly houses bacteria; that bacteria converts ammonia from the fish waste into forms of nutrients for plants; water exits the bio-reactor and is dispersed through trays housing plants, which take up the nutrients. The water then falls back into the fish tanks so clean that it makes for happy, healthy, hungry fish. We feed the fish and thereby keep the whole cycle going.

One of the 200 gallon fish tanks in the Aquaponics Greenhouse.

Our system is in a small, 12’ x 25’ greenhouse divided into two sides of two trays each. One side consists of a tray with hydroton, which is expanded clay balls, ($300.00, available from hydroponic suppliers), the other tray is a raft bed, made from foam insulation that floats on the water. Plants are stuck into 1” holes in the foam so their roots hang in the water. The other side is the same, except we substituted ordinary limestone gravel ($15.00) for the hydroton. Air is pumped into the fish tank, the bio-reactor, and the raft tanks. The only inputs are fish food, small amounts of a few nutrients, organic pest controls like insecticidal soap (used sparingly), electricity for the pumps, gas for the heating system, and water.

Happy plants in the grow beds of the aquaponics system.

Why It Works

As a horticulturist who has studied roots and soil and how air and water and nutrients all work together to make plants grow, I still consider aquaponics a weird kind of alchemy. I cannot wrap my head around the idea that roots, which would rot at the drop of a hat in wet, mucky soil, can thrive in a tank of water. Sure, I know there’s plenty of oxygen in that water, and, true, without soil there are no soil-borne pathogens in the system, but, still, sorcery of some kind or other must be at play!  But that kind of thing has never bothered me very much—could never understand why Darren held onto his ideals with such a blind death grip on Bewitched and didn’t just go with the flow. Seriously, a twitch of the nose and you’re living the dream on the French Riviera? Fool! He caused so much stress in their lives. Anyway, fact is, aquaponics works and it works pretty darned good.

In our next and final episode, we’ll reveal the “Lessons We Learned”, which, although fulfilling, will leaving you wanting more.