EHEIM climacontrol+ chiller and heater, 500 to 2,000 L

The volume of your tank gives the first guideline: up to 500 litres for the S, 1,000 litres for the M and 2,000 litres for the L. The difference between the room temperature and the water temperature also matters, because it is what makes the chiller work. For a 400-litre trout tank kept at 14 °C in a room that reaches 25 °C in summer, the 11 °C difference is significant, and the M offers a margin that the S would not have at the height of summer. A 300-litre tropical tank at 25 °C, in a temperate room, is fine with the S. Above 1,000 litres, or for an 800-litre tank kept very cool in summer, the L takes over.

Connect the unit to the return pipe of an external filter, in 16/22 or 19/27 mm, and check that the flow stays within the range of 500 to 800 L/h; a shut-off valve on each side lets you disconnect it without draining the circuit. The S measures 31 x 31 x 45 cm and weighs 17 kg, the M is 49 cm high and weighs 18.7 kg, the L is 53 cm high and weighs 19.7 kg. In operation, the noise level is around 47 to 54 dB at 80 cm.

In Europe, water temperature follows air temperature throughout the year. An outdoor pond, an above-ground tank in a greenhouse or a tank set up in a garage can exceed 25 °C during a heatwave, then drop below 10 °C in winter. For fish that tolerate only a narrow range, this seasonal swing determines growth, and sometimes survival, as the article on choosing fish for aquaponics explains in detail. Because it cools and heats on the same circuit, the climacontrol+ keeps your system at a fixed temperature all year round.

Salmon aquaponics, that is, the farming of salmonids in aquaponics (trout, salmon, char, grayling), is the most demanding case. These fish are poikilothermic: their body temperature follows that of the water, and their metabolism with it. The rainbow trout, the most widely farmed of them, grows best between 13 and 18 °C. Above 20 °C, it feeds less well and shows signs of stress, and the brown trout or the brook char, which are more sensitive still, should not exceed 16 °C.

Heat becomes truly dangerous because of the dissolved oxygen. Warm water holds less of it: at saturation, freshwater contains about 10.1 mg/L at 15 °C, 9.1 mg/L at 20 °C and 8.3 mg/L at 25 °C. At the same time, the fish breathe faster and the filter bacteria consume more. Since salmonids need at least 8 mg/L to be comfortable and suffocate below 6 mg/L, water approaching 23 to 25 °C in a heavily stocked tank can wipe out an entire stock within hours. The climacontrol+ email alert warns you as soon as the water departs by 2 °C from the set point, which leaves time to act well before the critical threshold. The guide to maintaining an aquaponic system in summer details the other precautions to take during hot spells.

With tropical fish, the constraint is reversed and winter becomes the problem. Tilapia grow best in water at 27 to 30 °C, stop feeding below 17 °C and die below 12 °C. As soon as your room cools down, the built-in 300 W heater takes over from the chiller, with no second device in the tank: the same unit holds the set temperature all year round, cool for salmonids and warm for tilapia.