I would be concerned about additives. For example, I am pretty sure water conditioners for removing chlorine/chloramine say on the bottle something along the lines of they are not for use on water being treated for plants that will be eaten.
I would imagine same goes for any other med/chemical treatment you may do on the tank.
"I laugh because I dare not cry. This is a crazy world and the only way to enjoy it is to treat it as a joke. That doesn't mean I don't read and can't think."
- The Number of the Beast,
Robert A. Heinlein