Can you post a picture of how the over flow is in your tank? Is it truly getting the flow off the surface? Some of the nano cubes weren't well designed in this regards.
Can you get a pic from the top down looking at the overflow area? It looks ok but just to be sure.
i blew that photo up and i see that the overflow is half loaded with debris...gunk...now my batteries are dead in the camera...its kind of a tricky thing....you want to have enough water in the tank so your not running low too often but if you fill it too much the intake bypasses the center charcoal and runs down the outer chambers where it is reintroduced into the tank....it looks like any possible fish oil from the frozen brine allthough rinsed can bypass the charcoal and filter medium.....which im trying not to use....but i may have to until i get the proper feeding down. and proper bacteria control
More surface movement won't help-I have the same issue exactly. Only thing that helps is a surface skimmer! Of any sort. For now I'm using a pre-skimmer box. I've allowed my water level to drop just enough so the water drains into the box and my pump carries it out. It's only taking the surface water-no more surface scum
Those are just extra proteins at the surface, a combination of powerhead or surface skimmer agitating the surface and a good protein skimmer should do the trick.
Sounds like you need more movement on the surface. I would point a ph up there to stir it up. should go away in a day or so with enough flow
i dont have a lot of movement more like lagoon. 2 heads at surface......i do have an extra powerhead.....just a little apprehensive to toss it into the mix most everything is doing well .....may try it anyways...especially pointed towards top.