A skimmer pumps air into the water in a needle wheel impeller pump
View attachment 32408775
This makes the water froth with bubbles. Proteins in the water stick to the bubbles and form a foam. The foam also captures particles in the water. Eventually the foam gets so large, some of it is pushed out the top and is captured in a cup.
This provides the nutrient removal for the skimmer.
Obviously, the skimmer aerates the water while it is doing all this.
It gives you some other abilities if you ever need them like removal of Chemiclean after a cyanobacteria outbreak treatment or capturing the goo that comes out of a biopellet reactor.
I have 2 very large skimmers in my system. One injects ozone into the water, and the other cleans and polishes it.
I am sure the opposing viewpoint proponent will show up here and tell you the evils of skimmers. To some extant he has valid points perhaps if you want a tank full of SPS but my system is mixed reef with a large angel and 2 eels and many other fish plus macro algae and corals. If your macro algae goes sexual and puts a mess into the water a big skimmer cleans it right up.
I think I would add a skimmer to my system just to have it in there even if I didn't want to skim. I would adjust it to not remove anything from the water. That way I could change my mind in the middle of the night if something happened and I decided I needed to skim. Plus you would get the aeration. I run bio-pellets and ozone.
Welcome to saltwater tanks. There are a few ways to do most things that will work. You can have a nice system with or without a skimmer. I cobbled together an overflow out of PVC pipe and added a 10 gallon sump to my 20 long tank with a skimmer a long time ago. I have had one in my systems ever since.
The Science of Protein Skimmers & How To Use Them
The Science of Protein Skimmers & How To Use Them | 52SE