Whats everyones favorite/ best way to get rid of/prevent a protein slick or a surface film?
I had a sponge filter in the tank that was causing enough surface agitation to prevent one, but I took it out and now the tank has a nice opalescent skim on the top. Canister's influent & effluent are both submerged and don't do anything to prevent it. I surface skim for my water changes but it comes back in a few days.

I hate surface film. Ever since i switched to an overflow, im so happy in not having to deal with one. But when i did, I had a lot of luck using a surface skimmer by Eheim. Surface Skimmer 350. Easy
to install and did a great job keeping the surface clear. You do of course have to clean it as it takes the skim and any floating detritus such as leaves.

If the film is not to thick then run a bubble stone or air stone but use a small amount of air to create small bubbles. This will break up the scum and prevent it from getting thicker.

Again the amount of bubbles does not need to be a lot. The smaller the better since bigger bubbles will start splashing small amount of water above the area where the airstone is placed then you have to end up putting some sort of cap on the area.

Surface agitation from a spraybar... or hob spillway, which ever is your preference

I just started feeding less and my problem cleared up with the amount of surface agitation I already have--no extra equipment required.

+1 on the Eheim 350. Bit pricey, but worth IMO. Air stones can do the job, but can leave water spots on bulbs, reflectors and trim.

Eheim 350 or ADA Vuppa. I have used both.

edit: nevermind!

The problem I have with a stand alone surface skimmer like the 350 is the evaporation experienced in the tank, as it's an open top (& I'm lazy and don't top off every day).

I wanted to avoid putting an airline in, thats the reason I took out the sponge filter in the first place, but it may come to that

I use the 350 in my 12g long and don't notice any additional evaporation.

Eheim skimmer's intake self-adjusts with the water level. It's an amazing product. I recently bought several.

I run a canister filter on my 55g planted tank, it the top is loaded with duckweed. i also keep the outlet of my canister filter pointed at the surface just a little bit to notice a small current, once the duckweed is established i don't notice any surface film at all, but also when i thin the duckweed out it also help take what ever film is there. having floating plants will help in the surface film. but on my 40g breeder i run a sump with a DIY over flow and it takes care for it for me.

would it be able to self adjust over a vertical distance of around an inch? Thats about how low I let it get before topping off.

The surface of the water is covered about 50% with amazonian frogbit, which is spreading, but the open areas are still enough to allow a nice film

I use a poppy type glass pipe (the spherical one that shoots water up), it causes a lot of surface agitation, the surface of my tank has been clear since I added it. I also have a regular lily pipe because the poppy pipe is designed to reduce flow in the tank

The vertical distance is about 2 inches.