Challenges of Recirculating Water

Although recirculating systems make up the majority of aquaponics units, there are a handful of drawbacks to returning water back to the fish rearing tanks. First, there are much higher chances of nutrient overload, and waste build-up problems, when the same water is used over and over again. Testing and conditioning are essential to prevent fish and plant loss, which interrupts the harvest cycle and costs you thousands of dollars per incident.

Second, recirculating aquaponics consume more energy because of the extra pumps required to operate filters and clarifying tanks. If you design an NFT system, you’ll also need a trickle supply pump for the plant growing trenches or pipes. Electricity costs can rise quickly when you factor in aeration and water heating as well. Finally, recirculating systems need plenty of filters and clarifying tanks to prepare the water not only for the plants, but also for it to return to the fish tanks. Only limited numbers of filters are needed for non-recirculating systems because fresh water is constantly supplied to the tanks. You'll still some amount of filtration in an open loop design, to ensure only a limited amount of solid waste is escaping with the water that leaves the system. Despite this filtration, there are still plenty of dissolved minerals that manage to reach natural waterways after a release from an open loop system.

Benefits of Recirculation

In contrast with open loop water systems, recirculating aquaponics incur much lower water supply costs. Few natural sources of water are legal to use or properly conditioned for the fish; resulting in the need to connect to a local municipal water supply or pay for water truck shipments. With recirculating systems losing as little as 1% of the total water per day to evaporation, it makes more sense for commercial farms that need to minimize costs. Recirculating aquaponics are also much more stable systems after being set up because the same water is used over and over, allowing for slow and gradual changes to pH and other qualities. Recirculating systems may or may not be more profitable than open loop designs, but they’re certainly more common. Finally, open loop aquaponics can create environmental issues if the fish waste causes algae blooms in natural waterways or overwhelms the holding capacity of the soil in nearby fields. Keeping the water within the system prevents these issues. If you have an excess of conditioned water, it will typically only be in the range of a few hundred gallons. This amount should be easy to pump by hand, to release into a relatively small field, without flooding plants or saturating the soil with too much of any one nutrient.

Challenges of Open Loop Systems

Some people who are interested in aquaponics think of open loop systems as being more natural, or somehow less expensive, if they have pond or creek available as a source of natural water. However, almost all water needs some pre-treatment before going into a sensitive series of fish and plant tanks. Pond and creek water often require more processing than you might expect. For an open loop system, even if you rely on a water supply from an urban or rural provider, you’ll spend hundreds to thousands of dollars on water costs each month. There’s also no way to capture excess nutrients and return them to the system or to another form of agriculture in many open loop designs. Finally, releasing hundreds of gallons of sewage per week results in added expenses, which can wipe out potential profits. If the wastewater from an aquaponics system is released into an existing water way, like a lake or river, algae blooms will result. These blooms deprive the water of oxygen and kill off fish and other natural aquatic life. Either way, before planning a business around an open loop design, you’ll need to secure a place for releasing the constant stream of water this system will produce.

Benefits of Open Loop Aquaponics

There are a handful of benefits of the open loop design that can make it worth considering for some specific situations. In very hot tropical conditions where heating is not required, open loop aquaponics, with freshly aerated water, can allow for an electricity-free fish and plant growing system. By diverting water from a well, stream or other steady supply, the water leaves the tanks and returns to the output zone before it loses its dissolved oxygen and becomes saturated with nitrates. The energy savings are not worth the cost of water and sewage in areas where there’s no free supply of appropriately conditioned water. Because these systems don’t need the same number of filters and settling tanks, they also tend to have smaller footprints than recirculating units. However, the amount of space needed for discharging the water can measure several acres, especially for large commercial systems releasing hundreds of gallons of water per day. Make sure to consider the costs of extra land or other storage and distribution facilities to compensate for the processing requirements.