From what I read and other people, Red slime usually cause by phosphate (forgot to mention, I also run phosban reactor)
The red slime can suffocate your corals too. Reducing light will starve algae!
Oh! try changing feeding. Instead of feed every other day, feed smaller portion everyday.I am guessing maybe you feed too much @ once and your fish did not eat all. Good luck...Hope someone else can chime in for more advices