Aquael Ultramax 1000 or 2000 external aquarium filter

In a tank where plants live off the fish's water, the baskets carry the nitrification. The bacteria fixed on the media convert the ammonia from the waste into nitrite, then the nitrite into nitrate, and it is this nitrate that the roots take up. You are therefore best advised to reserve most of the baskets for biological media and to keep only the top basket for mechanical finishing, avoiding chemical media that would hold back some of the nutrients. Rinsing is done with water from the tank and never with tap water, because the chlorine in mains water destroys the colony that took several weeks to establish. The article on the nitrogen cycle in aquaponics explains these steps in detail.

For a 250-litre aquarium stocked with about fifteen goldfish, the 1000 version is sufficient, and its prefilter catches the waste before it reaches the biological baskets. A grow bed of salad plants placed 50 centimetres above the water surface is well within the 1.9-metre limit, so the return flow can feed it directly before going back to the aquarium by gravity. To size the rest of your setup, see the guide on how to build an aquaponic system.

The tank is primed via the head system: you open the two ball valves, operate the primer a few times, and the water fills the filter without your having to suck on a pipe by mouth. For cleaning, these same valves are closed and the head can be lifted off with the pipes left in place, which avoids emptying the line each time. The prefilter catches the coarse dirt ahead of the baskets, so rinsing this prefilter alone spaces out the cleaning of the biological media. The ceramic rotor shaft is suitable for both freshwater and seawater and keeps operating noise down.

In the first month, a new tank carries almost no bacteria yet. Nitrification becomes established gradually on the ceramics, and the ammonium level, then the nitrite level, goes through a peak before falling. During this period, rinse only the pre-filter, feed lightly and measure ammonium regularly: the NH4 ammonium drop test tells you when the biological filtration has taken over and the tank's population can be increased.

The two tanks have the same footprint, 27 centimetres by 29, and differ only in height: 40 centimetres for the 1000, 51 centimetres for the 2000. Measure the clear height under your cabinet before ordering, allowing an extra ten centimetres or so to lift your head out during maintenance. The two pipes supplied, 1.5 metres each, can be cut to the shortest length needed, with no loops or tight bends, to preserve the return flow. If your setup requires sending the water higher than the rim of the tank, for example to a grow bed placed above, the head height tells you how far the pump will still push.