I think you need a little more water. It's tricky to get the initial balance. You need enough to get the mini waterfall effect through the InTank (so that there's real movement and flow from the display into chamber 1), but not so much that there's a negligible difference in water levels between the display and chamber 1. I dialed mine in during a water change - I filled it so that I could plug in the pump and circulate water and then I used a cup to slowly add 6-8 ounces of water at a time until I had it just right.
What you've done should get rid of the film in an hour or so since it's dropping off from display to chamber 1. However, you're not really forcing the water into the chamber the way you want to be doing it and with a little evaporation, you could find yourself draining the sump which would be bad.
Here's my return setup in the EVO (I think we have the same tank). You can see that the water is moving swiftly from the display, through the overflow, and down into the chamber 1 basked creating a little waterfall. It's not a massive drop, only 3/4 inch or so, but it's enough to keep the surface clear.
A skimmer would also take care of the issue. But in these tiny nanos, I don't think they're necessary (assuming you're doing water changes) and they present their own challenges.
Thanks for such a detailed reply man. That (including video) is exactly what I needed. I’m going to put slightly more saltwater in.
Definitely hard to find that balance. A little too much and the overflow level is pretty much equal to DT.