Overstocked ?

[Raptor]

Hey all just a quick question, I have a 240 gal that has been up and running for about a year now, lately my cyano and gha is getting out of hand. And curious to see if over pop could be my issues. Here's the lineup
Sailfin tang
Achillies tang
Yellow angel
Koran angel
Blue tang
2x clowns
Blue line angel
Fox face
Crosshatch trigger
I do weekly 20% water change with RO, and get decent skimming.
Thanks again