Yes you can bleach the decorations, use a 1:10 solution of bleach and water, allow to soak, until they are no longer green. It may work, it may not....Make certain that before you place them back in the aquarium, you soak them in bleach free water, and add about 3-5 times the recommended amount of dechlorinator (this is overkill, but where bleach is concerned, I'm a "better safe, than sorry" kinda person). You can bleach the aquarium in the same way, but your cycle will start over, the fish should be removed, (actually, you could remove the filter too, keep you from re-cycling), add bleach to make a 1:10 solution and allow to soak. Again, make certain you dechlorinate, before adding the fish back, you should not be able to smell the bleach when your done.
I would not use oxi-clean on my aquarium. We use it here, for our clothes and it is a soap, soap is toxic to fish, and I do not see how you could be sure there was no residue left when you were done. I think the bleach is a safer way to go, if you do it.