EHEIM shut-off tap for aquarium pipe, single or double

The diameter is read off the pipe: 12/16 mm means 12 mm inside and 16 mm outside, and the tap must carry exactly the same. The EHEIM classic external filter, for example, uses 12/16 on its 250 and 350 models, while its 600 model draws in through 16/22 and returns through 12/16. Large filters and pond pumps move up to 19/27 or 25/34. The double tap is fitted once per pipe, so twice on an external filter: one on the intake, one on the return.

When fitting, you push each end piece into the pipe as far as it will go, then tighten its ring or a clamp over it, depending on the diameter. Leave the dial accessible, on the side where you can reach in. The double tap should be placed where its two halves can pull apart without tugging on the pipe, ideally halfway between the filter and the tank, and never against a wall that would get in the way of the separation.

Take an external filter fitted with two double taps, one on the intake and one on the return. Disconnect the filter, close the four dials, then split each tap in two by loosening its central fitting. The halves on the tank side stay on their pipes, full of water; the halves on the filter side stay on the filter. You carry it to the sink without emptying the pipes, and only the few drops from the fitting need wiping up with a sponge. When you come back, push the halves together, open the taps and reconnect: the water left in the pipes avoids any need to reprime.

To adjust the flow, always work on the return, the pipe that sends the water back to the tank. Closing a tap on the intake makes the pump run dry, which wears it out and can make it overheat. A quarter turn is often enough to calm a current that is too strong for fish that prefer still water, or to stop an outlet splashing water out of the tank. Note the position of the dial once you have found the right setting: after cleaning, you will find it again at the first attempt.