Sicce Mega Filtra external aquarium filter, up to 950 L

The set of media supplied covers these three functions as soon as you open the box: foams, activated carbon, zeolite, ceramics and a finishing floss. Setting up therefore requires no additional purchase, and the first replacement only comes after several months, when the carbon is saturated. You then keep control of the composition, since the baskets accept biological filtration balls just as well as ceramic pre-filtration noodles sold by the litre.

The 950 SDC version stands out with an adjustable-flow motor, controlled via Wi-Fi from the CONTRALL app. You change the flow from there without touching a valve, for example to calm the current while feeding or to increase it when the tank is heavily loaded. Its head height also reaches 3 metres, compared with 1.9 metres on the 650 version. This height matters as soon as the tank is placed on the floor and the grow bed sits on a tall piece of furniture, or when part of the circuit returns water to a grow bed placed above.

In a system where crops live off the fish water, the stages are not equal. The biological stage produces the nitrate that the roots feed on, and it needs to be developed. The chemical stage does the opposite: carbon and zeolite retain dissolved compounds, and zeolite notably fixes ammonium, which is the raw material of nitrification. In an aquaponic circuit, therefore, replace the zeolite with additional biological media and keep the carbon for the end of treatment courses, when the aim is precisely to remove the product from the water. The pre-filter remains useful in every case, since it removes particles without retaining anything dissolved. The article on the nitrogen cycle in aquaponics explains in detail what the bacteria on the ceramics do.

On a 600-litre aquarium connected to a grow bed, the 650 version is sufficient in terms of volume, and its head height of 1.9 metres allows the return to be sent to a bed placed 60 centimetres above the surface, from where the water comes back by gravity. Then fill with Bioker ceramics the basket that used to hold the zeolite, and keep the carbon out of the circuit until the next course of treatment. The guide to building your own aquaponic system explains this set-up in detail.

The 650 version measures 26 centimetres by 26.5 and is 41.1 high, while the 950 SDC is 49.5 centimetres high on the same footprint. Both connect with 18 millimetre internal-diameter pipe, and their power cable is 2.2 metres long. This cable length often decides the positioning: a socket more than 2 metres from the cabinet calls for an extension lead, which should be fixed high up, away from splashes. Measure the free height under the aquarium, then add the clearance needed to open the head, otherwise every maintenance session will begin by taking the tank out. You can also place the tank next to the cabinet, as long as it remains below the water level of the aquarium.

The pre-filter is the only part that needs rinsing often, as soon as the return flow visibly weakens. Switch off the power, close the fittings, take out its basket and squeeze the foam in a bucket of water taken from the aquarium, before refilling the canister using the quick priming function. The other baskets are opened less often: the carbon is changed when the water takes on a tint again, the zeolite once it has bound all it can, while the Bioker ceramics are rinsed and never replaced. Rinse only part of the biological media at a time, to preserve the bacterial colony.