A garden pond, like aquaponics, represents a symbiosis between plants, bacteria and animals. For a number of years I have had an ornamental pond (cc. 4500 l) in my garden. The pond system is composed of a smaller pond which contains a homemade filter and a plant filter, from where water runs down a waterfall into a bigger pond with fish. This spring I decided to upgrade my filter to an aquaponic grow-bed.


 

From larch wood I constructed a 220 x 60 x 40 cm grow-bed situated directly over the top pond. Water does not flow directly to the grow-bed, first it runs through a pre-filter for mechanical filtration, this way fewer solids accumulate in the grow-bed. An aquaponics grow-bed with the ebb and flow bell siphon acts as an excellent biological filter. Expended clay pebbles have a large surface area for bacterial colonization. The continuous flood and drain cycle provides an oxygen rich environment crucial for the efficient biological filtration.


akvaponika okrasni ribnik


 

In late March I planted the first plants: strawberries, mint, lettuce, chives and other herbs. After good initial growth, the first signs of nutrient deficiency started to appear on some plants, especially those related to iron and potassium deficiency. I added iron with foliar treatments, but I decided not to supplement any other nutrients this season. In a garden pond system control of nutrient levels and water parameters is even more complicated than in the classical aquaponics system, which is a more closed system. First of all, in heavy rain periods a lot of pond water with nutrients simply overflows (dilution).


akvaponika okrasni ribnik

 

Furthermore many more factors influence the availability of nutrients to vegetables compared to “normal” aquaponics, where input is the main factor in bulk fish feed input is the main factor. In a pond we have constant decomposition of dead pond plants and leaves from surrounding trees. The presence of animals and other organisms involved in complex ponds nutrients cycles is much more pronounced. For example, every spring I have an invasion of frogs which reproduce in the pond and literally hundreds of small frogs jump into new life from the pond a few months later. Last but not least, all the pond plants and algae “steal” the nutrients from the vegetables in the grow-bed. Because of all the above mentioned reasons, a healthy garden pond is a much more complex eco-system compared to a “classic” aquaponics garden. Pond is also a more “robust” system in terms of water parameters for fish and can withstand bigger mistakes (e.g., too much fish feed), but on the other hand it is much harder to achieve optimal parameters for good vegetable growth.  

 

akvaponika okrasni ribnik

 

For better growth of vegetables I could just simply remove most of the pond plants. But this would lead to less shade over the water, more nutrients and definitely problems with algae blooms and possibly water quality for fish. I could also try to increase the feed input and the amount of fish. I have done an estimation of the plant growing area with all the pond plants included and calculated the needed fish feed input (for nutrients) and the amount of feed is just ridiculous. The pond is already fairly packed with fish; it would be impossible for me to overwinter that many fish in my ponds. To overcome this problem I will try to grow some edible fish (trout and carp) next season.

 

In a garden pond with aquaponics we face a paradox, on the one hand we want very low amounts of nutrients to prevent algae growth (especially phosphorus (P)), but on the other hand we need sufficient amounts of nutrients for good vegetable growth in the aquaponics grow-bed. Potentially we could overcome this with a very shaded pond and/or the usage of UV sterilization to prevent algae growth. Overall this year’s produce from the aquaponic grow-bed was hardly a horticultural achievement, but I am very satisfied with the water filtration function and the visual appearance of the grow-bed.

 

 

 

Author: Kevin Hartman