I take a cup of tank water, & mix it in the cup of water before pouring it in the tank. I use a 10 or 20 gallon to med fish, you may want to mix it in with a few cups having a larger tank.
That's a pretty good diet, might be a little protein heavy though. Try to mix some veggies in, along with a pellet food that's got some vitamin enhancement to it. I've heard of oscar keepers using liquid Centrum, a vitamin suppliment for humans, on cichlid pellets. As well as being part of a solution for HITH in oscars, it is good preventave medicine.
I've got a 5" oscar that gets beefheart, bloodworms, Omega One pellets, and zuccini a couple of times a week. Every 2 or 3 weeks he gets angel culls from my breeding setup. He also likes the spirulina disks and veggie pellets that are supposed to be for plecs. Oscars are not strict piscavores, they need some veggies to keep their digestive system running smoothly.