Backyard Aquaponics
A place to discuss aquaponics

Has anyone else experienced this? I set my pump up in the ST to pump into the FT, with the end of the pipe being maybe 12 inches below the surface of the FT (just a dry run, checking for leaks, etc).

One evening, I turn the pump off, and go to bed. Next morning, the FT has lost 12 inches of water, the ST is full to the brim, and about 150G of water has spilled onto my lawn.

I've never read anywhere about a pump possibly acting as a siphon once turned off. Is this common? Is it due to how I set up my system? Is there a simple check valve that people here recommend?

The head pressure in your Ft was enough to overcome your pump. Until air was able to get in and act as a siphon break. Is there a reason that you wanted to place your pump outlet 12in below the FT surface? If the pipework runs over the lip then back down to that height. You could just drill a hole in it just below your current waterline to give you an earlier siphon break.

That will always happen, you're lucky that the inlet pipe wasn't down on the bottom of the tank.

Always keep the the inlet pipe end somewhere near the top if the pump is below the water level or it will siphon to the level of your inlet pipe. If it's only 12" and your sump will carry that amount of water without overflowing it's not a major problem. A venturi would help stop any siphon but I'd still keep any inlet up near the water level the last thing you want is dead fish.

The same thing happens in an aquarium fish tank if the pump is lower than the water level.

Some people place their pump underneath the aquarium tank and then have a power outage come home and wonder why the carpet's wet.

I guess you could put in a T with a vertical riser with a drilled cap to above your FT full level similar to some SLOs to prevent siphoing.