Shortly after I posted the video at this thread

http://www.houstonfishbox.com/vforum...iphon-overflow.

I received a question from another Box'er asking how much flow a 1-inch siphon utube can handle. I already had all my stuff in the driveway, so I ran a test. Here is video showing the test.



Here is the answer.

When a siphon is setup, the siphon will seek a balance (equal water height) on each side of the siphon. When the water level in higher in the aquarium, water will be pushed to the box on the outside of the tank. The higher the water level in the aquarium, the faster the water will flow.

Based on my test, here are the results.

0.3" -> 135 gph; 0.6" -> 199 gph; 1.0" -> 258 gph; 2.2" -> 423 gph

Here is the rating curve:



I would say that you can reasonably expect to move about 500 gph per siphon tube depending on how much head (water height) difference your aquarium and overflow box can tolerate.