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Lessons Learned from a Year of Aquaponics

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.

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!

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.

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.

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.

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