So I don’t run a skimmer and to be honest I don’t want one - I run Berlin style filtration just relying on flow and live rock. The total equipment for my tank is a light, heater and wavemaker. It’s a glass box with no filter section etc.

Now I do get surface scum, not a lot but I do get some and I came across the below and I’m wondering if it would do a job of keeping this at bay… I can’t find much about it’s use in marine environments so thought I’d post here for opinions?

https://youtu.be/WNcoSOk81vM

If your tank doesn't have an overflow into a sump as you say, (if it did, the water level would remain perfectly consistent as it's the level of the sump's return pump section that drops with evaporation) then this gizmo will likely end up spraying micro bubbles everywhere when the water level drops starving it of water.

Might not be a problem but worth considering before spending any money on something.

Should be pretty straightforward? Fresh water tank in the cabinet and delivery tube and sensor wire running up to the tank?

The danger of having ATU sensor in the display tank though is it getting jammed on by a snail or something. I’d only have an amount of fresh water available I wouldn’t be too worried about the entire lot getting dumped in, and or some sort of cage around it.

You can get ATUs with two sensors IIRC where both have to agree to be on before it’ll pump any water.

I 3D print stuff though so I’d print a mesh cage to keep critters away from the sensor, magnetically attached to the rear glass.

Different setup system I got but I’ve not used a protein skimmer for donkeys years.
Mine is live rock , internal filter and a external filter, with a surface skimmer attached to internal filter , works fine and have nice clean water ,
Dave