Slightly altering the pH with the addition of a CV merely makes the water less hospitable to some microbes while making it more hospitable to others. Grandpa'd oh, few of those others should naturally be in your water supply, but the amount of a CV added to a gallon of water hardly moves the pH...
Elemental copper is an antibacterial. In small quantity, its not only safe, but necessary.
That said, there is very very little copper left in a modern penny, a lot of things much less palatable in a penny (or on it), and - once a layer of surface oxidization forms - no copper is exposed to...
Algae is a problem with your water. Potentially aggravated by your buckets. Its not generally a problem unless its affecting the function of your nipples. I know its not great to look at, but in nature, your birds experience a lot of it.
Galvanized buckets I avoid on (numerous) general...