@leahfiish,
I might’ve missed it in the photo but do you have an airline drilled and tapped into your secondary? (Open channel) If not, and if the waterline isn’t above the opening of the open channel, then you have a siphon trying to operate as such mixed with air. Further, looked closer at your pic and as I believe MWzl mentioned, your open channel is hovering over your siphon, which
could potentially be creating a suction upwards toward your open channel( I say could, because that phenomena would land in the realm of physics of which I haven’t encountered, since I’ve never seen anyone plumb their OC directly over their siphon before) I would first drill and tap an airline in the OC, see if that solves the issue, and if not, move the elbow away from your siphon. As long as you don’t have an air leak in your siphon and the standpipes aren’t submerged beyond approx an inch into your sump waterline, that
should solve your issue. In your sump, hold your hand under the “secondary.” Is it acting as the siphon?