Welcome!!!
For that bell, there are a couple of things you might try. I'd start simple. Make sure you have a large enough notch/cut-out on the bottom of your bell to be sure enough air gets in to break the siphon. apart from that, if you are feeling really industrious, you could try the 'better bell' which is I think and Affnan development...?
http://www.affnanaquaponics.com/2010...s-of_9459.html
https://www.youtube.com/watch?v=BzKUzcdeaI8
And again, WELCOME!!!