I would like to see if i have enough filtration for Oscars?

i feed my 3 Oscars several times a day as reccomended by the directions on my Wardleys floating cichlid pellets, and my water is kind of cloudy after i change 30% water every three days , I have 2 (HOB ) filters 1- Marineland Biological filter filtering 400 GPh and a whisper 60 filtering 330gph. do you think that i may need a undergravel filter for a 55Gal tank