not new, but, loop siphons

[joebob]

Hey All,

I have a system that I am currently building (pictures attached). A total of 440 gallons of water. A pump that is moving water at approximately 86 gallons per hour at about 7' of head.

Two grow beds. For the top bed, I am using a classic autosiphon. On the bottom bed, I am using a loop siphon. The loop siphon is having issues; for example, even when the bottom bed is almost completely full, I am not seeing any water in the tube.

All fittings for the loop are 1-1/2", while the pump delivers water through tubes that are 3/4".

Anyways, it would be great to get some suggestions from folks; I have a few ideas as to why the siphon might not work in practice just based on comparing a few things to a few pictures, but I dont want to make any major changes until I get a bit of insight from folks.

Thanks!

Joebob