Aquaponics – part IV
In the previous three posts I shared more about our little backyard aquaponics project. The pictures show a lot, although they are written in Dutch (I lost the English translation). In the few months since the last post I’ve learned a few more things. I’ll spread them out over a few categories:
The system
The beauty of a simple system is that not much can go wrong. I didn’t encounter many issues in the first months. But after a while a bit of fish droppings started to accumulate at the bottom of the tank and the water got more murky and algae started growing. One trout floated dead on the water surface that week, although I’m not sure what the reason was. The readings for the water quality were still perfect. From that point onward I fed the fish less per day and that solved it. But its still necessary to use the net to collect some waste from the bottom of the tank every now and then. This could probably be solved in a system where the pump is not in the fish tank and the overflow pipe sucks in the water from the bottom of the tank. I have the pump float just under the surface, so it doesn’t get clogged all the time. But even then that happened twice when the fish droppings were more stringy for a few weeks.
Once we were gone for four days and asked someone to feed the fish and use the net for cleaning the bottom of the tank if needed. When we returned we found that he had managed to pull out the water hose twice and had loosened the air inflow point from the side of the tank without noticing. Three of the seven remaining trout died due to lack of oxygen, sadly enough. Lesson: give better instructions. This made us decide to harvest the other four trout before we go on a one month trip next week and to close down the system for the winter.
The water quality has stayed well and the readings are good. There should be enough nitrate in the water, but some plants in the middle of the grow bed seem to get less nutrients, while much fish droppings remain in the tank. Could it be that a ‘floating’ pump doesn’t pump all nutrients around so well?
The pictures below show the system with a bamboo balcony screen around for prettiness sake and a frame above for the tomatoes. During a heat wave last month I put blankets over it and turned off the pump, to keep all water together in the tank. Less nice for the plants, but it really helped to keep the water cool. It only warmed up 2 degrees Celcius per day while the outside temperature was quite a bit above 30 degrees. Twice that week I drained out most water to replace it with colder tap water, to keep the temperature under 23 degrees. I read that trout dies at over 24 degrees.
The fish.
So sadly enough half of them died before their time, but three of those died due of human error that could have been prevented. They have grown well and seem to thrive in the tank. They are curious and active and always come to take a look when I open up the tank. Food disappears in no time. I feed them less than 1% of their bodyweight per day, as the water becomes too dirty if I feed more. I will know their weight and length next week after ‘harvesting’.
In the week before the heat wave one trout started to get some kind of mold or infection, and some others caught it too (see picture). I put two kgs of salt in the tank and that helped get rid of it. After one week they all looked fine again. The same trout had a bleeding lip, which very slowly healed. I’m not sure what that was.
The plants
Almost everything grows well, except the broccoli. Those little plants never developed well, so I took them out. I put in many seedlings just to try which ones grow best, but it seems to slow down their collective growth, as they don’t have enough space to catch the light then need. It’s been a while since I had a garden, so I’m learning here!
The strawberries really suffered from the salt in the water. The zucchini was planted in the wrong corner, too close to the tomatoes, and didn’t get enough light and space. After I moved him he died, as he lost quite a few of his long roots. Of the two cabbages that I planted the one closer to the middle grew as fast as the other, but had a lighter color leaves. He visibly got less nutrients than the other one that was closer to the pipeline on the outside from where the nutrient-rich water drips, and therefore filters out most of the nutrients.
I had a bit of caterpillars on the cabbages and cauliflower. I used some essential oils and that helped, and I removed a bunch by hand. The oils also worked well against lice on the herbs.
Some plants had lightly colored leaves. After adding chelated iron to the water this improved.
The harvest
What we harvested tasted good! The peppers were small, but tasty. The mint had a good taste, as well as the chives and parsley, although the parsley leaves often stayed light green instead of their normal darker color. The endives were good and big. The first tomatoes are almost ready for harvest. The cabbage and cauliflower will not get ready, as we are shutting down the system next week. The carrots couldn’t push away the medium well enough and stayed tiny. One started to rot and a few others split open. But their taste was good.
Evaluation
All together I’m quite satisfied with this experiment. It’s not very hard to keep the system running and even with the lower amounts of sunlight in our backyard we were still able to grow quite some vegetables. But the plants didn’t grow as big as for example in the garden of my parents. An earlier start in the year, a warmer location and more experience in gardening will probably each play a role in that difference as well!
Financially it cost me a bit over €300, including petrol costs, fish feed etc., just as I had budgeted. We got a few bucks worth of vegetables and some fat trout in return for that (it could have been seven of them). To recover the costs in a few years you would need to add a few more grow beds and some more trout, which we can’t do in our small backyard. And in the Dutch climate it is almost necessary to have the system placed in a greenhouse to extend the growing season. But the main benefit for me certainly has been that it is satisfying to try it out and to work with the fish and plants.
To be continued – next week the harvest!
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