Well, I sure appreciate the suggestions. I watched the videos and fiddled around some more with the flow but still no luck. I was struck by his design, he doesn't use an airline tube at all. I wonder if I should just redo the siphon following his method.

I think it may be the siphon itself that is causing all of the problems. I could put a balance line between the two but if its the siphon with the problem then that won't make a difference. Changing the flow rate doesn't seem to make a difference. The one that works, is consistent no matter what and the other one never breaks.