EHEIM TWINfeeder automatic aquarium feeder, 2 x 80 ml

The random feeding function dispenses food at a time picked at random between 8 am and 6 pm, rather than at a fixed time. Fish that are always fed at the same time learn the rhythm and gather under the hatch before the meal, which always favours the same individuals; an unpredictable time spreads the food more evenly between the dominant fish and the more timid ones. The pause mode, for its part, suspends all feeds in a chamber for 24 hours after 6 days of operation. This gives you one day without food each week, which allows the fish time to digest, without having to reprogram the unit.

The physical separation of the two chambers matters as much as their programming. Two feeds mixed in the same hopper sort themselves by grain size, so that the auger no longer dispenses the mixture in the proportions you intended. With two sealed chambers, you get in the tank exactly what you poured into each hopper. The chambers take most commercial flakes, sticks, granules and tablets, but never a fresh or moist food, which would stick to the auger. Both hoppers are ventilated, which limits the food caking under the effect of the humidity from the tank. Fill them two thirds full rather than to the brim, so that air can circulate above the food.

The dose is set in screw turns, and each chamber keeps its own setting. Start low, trigger a manual feed over a sheet of white paper to see the actual quantity, then watch the tank 10 minutes after dispensing for a few days: if food is left on the bottom, take one turn off the chamber concerned. Repeat this check at each change of season if your tank is not heated, and every time you add or remove fish, because a dose that suited six fish is too much for four and not enough for ten.

The dispenser attaches to the lid or the rim of the tank with the two hook-and-loop straps supplied, and it also fits the feeding openings of EHEIM VARILUX lids. Place it above two areas of open water, away from the filter outlet and the air diffuser, since the electronics must be kept clear of splashes and humid air, even though the buttons withstand sprays. To clean it, remove the hatch cover and then the screw, clean the chamber dry, and refit the screw by turning it gently until it clicks into place.

In an aquaponic system, all the feed given, whatever the compartment, ends up as nitrogen that the biofilter has to process. The benefit therefore comes from better-distributed feeding: fewer pellets sinking to the bottom uneaten, so less decomposing organic matter and a biofilter that receives a steadier load. The mechanism is explained in the article on the nitrogen cycle, and it can be checked with an essential test pack, with ammonium and nitrite staying low when the ration is right.

The feeder is also useful during an absence. Programmed for 1 meal per day and per compartment, with a smaller dose than usual, it keeps your fish going without loading the water, and the pause mode gives them one day without food each week. Run this programme for a few days before you leave, to check the quantity and the state of the batteries while you are still there. The other precautions are gathered in the guide to going on holiday with an aquaponic system.