Will treating eggs W/Methylene Blue harm adult Oscars?

No, they will just be bumping into each other:lol:

Personally i dont really think you need to put methylene blue in the tank with the adults. It is normally used to stop the infertile eggs fungusing up and turning all of the others bad. That job is done by the adults looking after the eggs by fanning them with their fins. Inevitably you will get infertile eggs but Oscars should get rid of those by eating them. If you watch the Oscars carefully you will see that from time to time the Oscar will move its eye down to look at the eggs and remarkably they can remove eggs one by one if they have to. If you do add it there is no need to add so much that it is really dark, just add enough to tinge the water blue. I have never added it to the adult tank just when i have removed the eggs to hatch them artificially.

were can i get methylyne blue???

Took me 20 seconds to find on the Internet. Obviously you might not be in the United States, I wase just showing how easy it is to find somewhere that sells the stuff

http://www.aquariumguys.com/methyleneblue.html

PS, only press the submission button once

I had a breeding pair of convicts once. They used to pick off the infertile eggs. As oscars are good parents like convicts I also dont think you would need to add the methylyne blue. Personally save your money and dont bother and see what happens. If the eggs get covered in fungus use the methylyne blue on the next batch of eggs