I don't know about oscars, but I usually put the frozen cube in a little bit of aquarium water to thaw and settle down, then I throw away the brown nasty looking water and rinse the food with aquarium water a couple of times. Then, I give it to my fish a small amount at a time. My lfs told me to drop the frozen cube directly into the tank. However, I found out that this way one or two fish will devour a big chunk before others can get to the food. By rinsing I am also sure that it's clean and the dirty stuff won't get into the tank. Hope this helps.