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

The tank volume gives the first guide: up to 500 litres for the S, 1,000 litres for the M and 2,000 litres for the L. The difference between room temperature and water temperature also matters, because it is what makes the chiller work. Take 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 in midsummer. For a 300-litre tropical tank at 25 °C in a temperate room, the S is more than enough. Beyond 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. Leave space around the casing, which releases into the room the heat drawn from the water, and never put it in a closed cabinet. Always store, transport and run the unit upright. The S measures 31 x 31 x 45 cm and weighs 17 kg, the M is 49 cm high and weighs 18.7 kg, and the L is 53 cm high and weighs 19.7 kg. When running, the noise level is around 47 to 54 dB at 80 cm.

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

Salmon-based aquaponics, that is, raising salmonids in aquaponics (trout, salmon, char, grayling), is the most demanding case. These fish are poikilothermic: their body temperature, and therefore their metabolism, follow that of the water. Rainbow trout, the most widely farmed species in aquaculture, grows best between 13 and 18 °C. Above 20 °C it feeds less well and shows signs of stress, and its lethal temperature is around 25 °C. Fish such as brown trout or brook char are even more sensitive to heat and cannot withstand water above 16 °C.

The main danger comes from dissolved oxygen. The warmer the water becomes, the less of it the water can hold: at saturation, fresh water contains about 10.1 mg/L at 15 °C, 9.1 mg/L at 20 °C and only 8.3 mg/L at 25 °C. At the same time, the fish's oxygen consumption rises, as does that of the filter bacteria. Salmonids need at least 8 mg/L to breathe without difficulty, and they begin to suffocate below 6 mg/L. In a heavily stocked pond, a single day of heatwave can therefore wipe out the entire stock, and with it several months of growth. This is where the climacontrol+ e-mail alert really earns its place: it warns you as soon as the water strays more than 2 °C from the set temperature, which leaves you time to act well before a critical threshold is reached. 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 it is winter that causes the problem. Tilapia grow best in water at 27 to 30 °C; they stop feeding below 17 °C and die below 12 °C. As soon as the room cools down, the built-in 300 W heater takes over from the chiller, with no need to put a second device in the tank. The same unit therefore holds your chosen temperature all year round: cool for salmonids, warm for tilapia.