I'll go so far as to say you'll cure the HITH with those water chanages alone. But of course I have no kind of scientific proof, just lots of reading articles.
I actually would be concerned with .5 cc every day being too much. The only basis I have for saying that is that I know humans can get too much of certain vitamins and more isn't always better (unless we're talking water changes). And keep in mind if you're giving him .5 cc that's the full amount that he's getting since you're injecting it in the worms. That's a lot of anything for a fish that weighs 1-2 lbs. I used to squeeze shrimp dry with a towel and then soak them in the VitaChem and feed them. That worked until several of my Oscars lost their taste for shrimp.