Plumbing: Siphon Breaks

Notice the small stream of water coming from the bend in the elbow

A common type of filter system on large tanks is a sump filter. 

It consists of a smaller tank that usually sets underneath the main aquarium.  As water is pumped into the aquarium from the sump, the water level rises then flows over into the drain and back down to the sump.

If the pump stops working, the water line going from the pump into the aquarium can start flowing backward causing a siphon.  If a check valve is not present, the water will keep siphoning until the end of the return pipe comes out of the water, allowing air to enter and break the siphon.  If the pipe is quite a way down in the tank and the tank is large, this can cause the sump to overflow. 

A cheap, easy way to help prevent this from happening is to create a siphon break in the return pipe.  This can be as simple as drilling a small hole on the underside of the return pipe at its highest point.  As water is being pumped through the pipe, it will spray a small stream into the tank.  When the pump shuts off, air will be sucked into the pipe through the hole eventually causing the siphon to break.

You can start with a small 1/8” hole and test the system, resizing the hole if needed.  Try to drill the hole in a piece of plumbing that can easily be replaced.

Check and clean the hole during routine maintenance.