You can't really use too much other then wasting money and the smell of vinegar will be stronger through your house/garage... not that vinegar is really expensive.
I usually use a gallon if I'm not in a hurry and the tank is going to sit anyways for multiple days. If you want want to speed it up... use more vinegar. Not all the salt-creep, coraline, and hard water stains will come off on their own. Sometimes after letting it soak in the vinegar for a couple of days you need to go in there and wipe off whats left with a scrubber pad. But at that point it should wipe off very easily.