Hole in the head PART 2

Ok. Here is where I would like to say yet again, I am green when it comes to being an aquarium hobbyist. I have gone to every local pet store (mom and pop) and no one has givin me the simple most obvious advice regarding my oscar and hole in the head. Not to mention that I have had another fish (blue devil) who has had a problem for some time and no one directed me to the solution. The blue devil has had almost a bubble under his skin and as soon as it heals another one appears somewhere else. He even lost an eye because of this. I treated my tank with melafix and it never went away, even though he seemed to be fine and the other fish were fine, the bumps kept appearing. With diligence I searched for a cure for the oscar as I am sick of hole in the head. I keep hearing its the water quality and I refused to accept that. When one changes the water every three days, goes so far as to pick up every dropping of feces on the gravel and added vitamin suppliments, one begins to feel as though the world is mad. Well with a search to the web and some serious reading I now know that it must be parasites. With the oscar and the blue devil. Say the water stresses them slightly... this makes the parasites multiply inside them and causes the hole in the head, the skin lacerations and so on. So there you have it. And the simple treatment is "Jungle Parisite Clear" or go to www.junglelabs.com. Drop in the pellet and it fizzes like Alkaseltzer. We have yet to see how fast or if at all my guys get well, but I am hoping and I feel sure this is the answer as I have tapped every resource. I just cant believe that no one in the pet stores mentioned this simple thing to me. So one thing you have to remember is this: many times people simply don't know what they are talking about. So before you throw chemicals in the tank and screw everything up "think parisite". NOT always bacteria or fungus. How does one know the difference between the two? I would have to say trial and error.