Convert-Swimming-Pool-Aquaculture - feat

Converting a Swimming Pool to Grow Fish

Aquaponics is becoming an increasingly popular method of permaculture, probably because it can start with a backyard swimming pool. While creating an ecosystem on one’s own may seem like a daunting task to many, one of the most appealing aspects of aquaponics lies in the fact that nature can do most of the work.

For suburban couple Les and Annette Mulder, the first step to farming one hundred fish in their yard was to stop pumping chlorine into their pool. While neighbors looked on with skepticism, the Mulders encouraged algae growth, welcomed the appearance of mosquito larvae, and even made use of a children’s pool to grow water chestnuts.


The bacteria and other organisms that began to grow in the pool played an important role in the cycling of the aquaponic system. Introducing a source of food for bacteria is crucial in establishing a stable aquaponic structure. Various methods for this cycling include using dead fish, feeder organisms, urea fertilizer, and even urine as a source of ammonia. The Mulders did not take up the so-called “peeponics” method involving urine, but instead used small Pacific blue-eye fish for their system.

The couple also utilized the filtration ability of aquatic plants such as papyrus, taro, and Louisiana swamp iris, growing them in three bathtubs filled with gravel. Just as the plants provided clean water for the fish, the fish provided nutrients for the plants in turn. Filtered water cycled through the “growbed” tubs and back into the pool with the help of a 60-Watt pond pump, which reduced the consumption and costs of both electricity and water, providing the couple with an added economic benefit.

Just five months after converting the pool, the silver perch that the Mulders decided to grow were completely capable of feeding themselves, living off of insects, plant shoots, and algae. Since Les expressed a desire to “get to the point where… it becomes self-cleaning and self-regulating,” he never feeds the fish himself. In letting the Perch thrive on what nature provides, Les and Annette’s 55,000-liter pool yields between 30 and 50 kilograms of fish each year. Les even thinks that the fish are developing at a faster rate than those fed with fish pellets for commercial use. But it’s not just the fish that benefit from natural food sources. Healthy Omega-3 fats will likely be passed on to the people who eat the fish, as some algae contain high concentrations of the fatty acids.

The appearance of the emerald-spotted treefrog was perhaps the biggest surprise in the Mulder’s aquaponics system. The couple was excited to find the frogs, “a species [they] never had around here before,” in the grow beds one day. This increase in biodiversity was yet another sign that the pool had become a successful ecosystem.

Geoff Lawton visits aquaponics system.

Aquaponic systems like the Mulders’ do, of course, benefit the fish, but are also advantageous to the plants and humans involved, as well as the environment as a whole. Commercial fish and plant farms are often unsustainable and can produce pollution in the form of pesticides, herbicides, and excess food, none of which play a part in aquaponics. Homegrown fish feed off of naturally produced zooplankton and algae instead of synthetic pellets, and are not overcrowded, which is often the case on commercial farms, where fish are more susceptible to parasites. Many larger farms also exist in the open ocean, where waste can lead to algae blooms and hypoxic dead zones.

Aquaponic systems like Les and Annette’s act as a hybrid of hydroponics and aquaculture, eliminating the nutrient cycling issues faced with the other two systems of sustainable agriculture. Growing fish and plants locally ensures that the owners can control and oversee all the farming processes, producing healthy fish in a sustainable manner. Between the financial benefits of energy conservation and the environmental benefits of sustainable growing, it’s really no wonder why aquaponics are gaining prominence in the world of modern permaculture.