It's not a 3" pipe, that's a two inch.
The fill height is not shown in pics. The siphons peak out at 2 inches below the surface edge of barrel. So the head pressure from the water volume in barrel initiates the siphon.
I will make one siphon the inverted U today as suggested, on one barrel and check results. I shut the system down last night with all barrels full. So will have to drain one.
Good point on the media.

Grow beds are filled by gravity. That's the reason why the IBC is elevated, it produces head pressure. As long as there's enough head pressure I have no problem filling the beds. I resolved this initial problem yesterday by adding a pipe to the intake so that it siphons from the IBC at greater depth. This allows for greater swing in water height in the IBC. When the sump is actually connected and in use, this won't be a problem.

I am on my way out the door now to start cycling again.
Thank you.

****Update****The U adjustment made no difference. U or M both are not working, and exhibiting the same symptoms. NOT cycling on and off the way they should.