I don't know if this sounds like botulism. I had a drake diagnosed with botulism a couple of years ago, and his primary symptom was progressive paralysis, starting with one leg, over a period of several days. He developed vertigo and couldn't hold his head steady or eat/drink easily, and at that point we euthanized him. Once neurological damage occurs it can't be reversed, so the treatment has to be started very early in the course of the disease. The good news is that it's relatively rare. If your bird is getting better rather than worse, my guess is that there was another problem (or the colloidal silver worked!). Could he have been affected by the heat?