EHEIM FLOW submersible pond pump, 3,200 to 15,500 L/h

A pond pump runs non-stop, so its power draw is best read as an annual running cost. The six models draw 55, 50, 70, 80, 110 and 160 W, in order of increasing flow rate, which comes to about 482, 438, 613, 701, 964 and 1,402 kWh over 12 months of continuous running. The FLOW 5000 uses 5 W less than the FLOW 3500, even though it delivers 4,600 L/h instead of 3,200 and its maximum head reaches 3.1 m instead of 2.9 m. If you are hesitating between these two models, the second therefore costs nothing extra to run.

The FLOW 6500 and 9000 share the same maximum head of 3.6 m, while the latter delivers 3,000 L/h more for an extra 10 W, or about 88 kWh more per year. To feed a large filter or a wide waterfall lip, that extra flow therefore costs very little. Conversely, a model that is too big for your pond runs all year for a flow you have no use for: start from the flow your filter or waterfall actually needs.

The FLOW 3500, 5000 and 6500 connect with 1 inch or 1 1/4 inch fittings, while the FLOW 9000, 12000 and 16000 also accept 1 1/2 inch. The stepped adaptor is in the box, and you cut off the part that matches your spiral pipe. The pump body lets through particles of up to 8 mm, which matters in a garden pond where leaves and debris always end up on the bottom. The housing around the pump retains larger debris, and it is the part you will rinse most often. The three small models measure 241 x 254 x 122 mm, the three large ones 267 x 300 x 130 mm.

In a system where fish, bacteria and plants share the same water, the pump carries the nutrient-laden water from the fish pond to the grow beds, day and night. Its power consumption therefore becomes a running cost that you know from the moment you buy. Two points should be checked before ordering: the model's maximum immersion depth, which must cover the depth of your pond, and the run of the 10 m cable to a protected socket. The guide to setting up an aquaponic system points out that the flow rate printed on the packaging is measured with no height to overcome.

Let's take a fish pond 1.50 m deep, whose water is lifted to grow beds placed 1.20 m above the surface. The FLOW 3500, limited to 1 m of immersion, cannot sit on the bottom, whereas the FLOW 5000 can, since its limit reaches 2 m. Its maximum head of 3.1 m leaves a comfortable margin above the 1.20 m to be cleared, and its 50 W works out at around 438 kWh per year. At the low point, your pump also draws in droppings and uneaten food, which its 8 mm passage carries to the circuit's filter, filled for example with biological filtration beads.

When the flow weakens, unplug the pump and lift it out of the water. Remove the pipe and the nozzle, open the housing by pressing its two side clips, then rinse it under running water. The impeller then comes out, after unscrewing the locking ring on the FLOW 3500, or the cover screws on later models. It contains a powerful magnet: grip it with pliers to avoid pinching your fingers, and keep it at least 30 cm away from a pacemaker. If the thermal protection has cut the motor, let the pump cool for about an hour before plugging it back in.

The pump operates in water between 4 and 35 °C. Before the frosts, take it out of the pond, clean it, then store it somewhere frost-free, preferably in a bucket filled with water, which avoids starting difficulties in spring. The plug, however, is kept dry. In spring, simply place it back on the bottom and reconnect the pipe, since the fitting stays screwed onto the pump from one season to the next.

The box contains the assembled pump, its stepped connection nozzle to be cut to the diameter you need, and its 10 m cable, permanently attached to the pump. No assembly is needed before placing it on the bottom, and the IP68 rating allows continuous submerged operation. The instruction leaflet, written in French among other languages, details installation, cleaning and winter storage, and the pump is guaranteed for 3 years by the manufacturer.