Good morning Carol.
I first noticed surface scum on my 29 tank I use to prefilter water for my water changes. It wasn't a great deal of scum but I could still tell that it was there, even with the AC 50 filter running. So I figured if I had surface scum there that I would have some on my other tanks mainly the gold fish tank. Sure enough I could see some so I added the surface skimmer to that tanks filter too. No more scum

My 265g tank has a
HOB over flow system so there is no scum there period

yeah!!
Wriggley's
betta tank doesn't have any scum and I don't use the surface skimmer on that tank.
Too, I have well water and I can see the silt as it settles and what doesn't sink floats and goes down the surface skimmer.
I can pull up Drsfostersmith.com with no problem but I couldn't get it to pull up the surface skimmer. I also tried a search by item # and it wouldn't come up.
Ken