I meant that I, in the present, "use" the Hikari pellets to feed my oscar...perhaps I should have worded it differently. Sorry about the confusion.
What size of pellets are you feeding him (i.e. small, med., or large?)?
One rule of thumb with regards to feeding, according to what I read, is to watch your oscar's belly. If it gets slightly rounded, perfect. If it appears to be bloated or bulging severly, then I'd probably cut back.
Another thing...
Don't bother dropping any sort of sinking wafers in for the pleco until lights-out at night. Try to 'sneak' them in where the pleco typically resides in the tank, and that way (hopefully) your oscar won't be as likely to gobble them all up. With any luck he'll be sleeping by the time you throw in some food for the pleco. Also, your pleco doesn't exactly look huge or anything, so adding wafers in for him every other night is probably more than sufficient.
With your oscar being at 5-inches in a 55 gal., you're really starting to get to the point where his nutritional demands will begin taxing your tank's bioload-handling capabilities big-time. I'm already starting to worry about how mine (also a 55 gal.) will handle the increased bioload as my fish grow. My plan is to have a 75 gal. for my oscar and pleco by Christmas at the latest (tiger barbs will have probably been eaten by then). Sorry to ramble on, lol.
BV