Don't press the suction cups to hard against the glass or they won't reduce the noise and vibrations from the pump. This will result in a clear humming from the aquarium and in some cases it will even make the lighting hood vibrate!

If you have a powerful external filter you must use the original intake together with the surface extractor. For this you can buy a special T-junction from Eheim. It has two 16/22 mm connections and one 12/16 mm connection.

Together with a valve between the T-juntion and surface extrator You can regulate how much water is to be taken from the extractor. This will make it less noisy because the water doesn't fall more than a few millimeters inside the extractor.

You can also close the valve at water changes and get rid of the problem of refilling it with water (if you lower the water level enough in the aquarium air is let into the extractor tube/hose and it's hard to refill).

Since none of the two reactors I use work flawlessly I am thinking of two other ways of getting the gas into the water: 1) by using an air diffusor, 2) by letting the gas bubbles enter the intake for the external filter. I will probably try this soon and then get back here with the results.

The diffusor will probably waste a lot of gas, but the gas is cheap. Letting the gas into the external filter will probably mean that all of it is used, but what happens to the "false gases"? And does none of the gas trickle its way up through the filter medium and then just flow out? Will the filter be filled with the non-CO₂ gases?