EHEIM LOOP pond filter with pump and UV-C clarifier

Before choosing, look at the space you have at the water's edge, because the four kits come in two tank formats. The 5000 and 7000 models share a tank measuring 400 x 315 mm at the base, 263 mm high on the first and 388 mm high on the second, and connect with 3/4 inch fittings. The 10000 and 15000 models share a wider tank of 603 x 398 x 368 mm, connected with 1 inch fittings. The pump changes with each model: PLAY1500 on the 5000, then FLOW2500, FLOW3500 and FLOW5000, with a maximum head height that rises from 1.4 to 3.1 metres. The FLOW pumps are protected against overheating if the water level gets too low. The pump cable is 10 metres long and the clarifier cable 5 metres, so it is this second cable that determines where the socket needs to be.

The fourth stage of the tank, the biological media, provides long-term purification. The bacteria that settle there convert the ammonia from the fish into nitrite, then the nitrite into nitrate, and this nitrate stays in the water. In an ordinary pond, it builds up and only goes down with water changes. In your system, if crops share the circuit, it becomes fertiliser for the plants, which take it up as it forms. This is also why you should treat this stage gently: an intact bacterial colony converts ammonia without delay, whereas media that has been thoroughly washed has to be recolonised. The guide to the nitrogen cycle in aquaponics details these stages.

The stages are not cleaned at the same pace or in the same way. The coarse sponge is squeezed out in a bucket of water taken from the pond as soon as the return flow weakens, sometimes every 2 weeks in midsummer. The fine sponge gets the same treatment, but less often. The biological media is barely rinsed, and never under a jet, because it carries the bacterial colony. Never wash all four stages on the same day, otherwise the biological filtration would start again almost from scratch. Spread your cleaning over 3 weeks, one stage at a time, and replace a sponge that no longer regains its shape with replacement sponges for the LOOP filter, coarse, fine or carbon.

As frost approaches, you shut down the circuit: the pump, the clarifier and the tank are drained, cleaned and stored under cover, since water trapped in a unit can split it when it freezes. The UV-C tube does not wear out during this shutdown, and the bacterial colony in the tank largely dies off. In spring, the restart is therefore a bit like a small commissioning, while the bacteria re-establish themselves. Concentrated pond bacteria added as soon as the water exceeds 10 °C shorten this period, during which the fish rations are kept modest.