Grrrrr, what gives

[IslandReefer]

Sounds like a normal day at the reef.
You may have some dead spots in your flow....=cyano.... combined with a touch of excess organics = green glass film.
Sooo maybe clean up best you can, ie tune skimmer, scrap and suck, change phosban,carbon etc, watch out for excess food......and /or buy some more snails eg Astras or Banded Turban snails (exact name escapes me).
My Tangs do a good job for me, with a few snails.
I think the important thing is balance...organic in = organic out or a close as possible.
Also I find that if my Alk gets low green algea is supported better....quick test and a Alk boost might be in order.
Just my 2cents...works for me

Good Luck