the vinegar would have caused a drop in alkalinity in addition the drop in pH. It wouldn't just be pH. Probably just not aerated well with a small surface area (in a barrel) and excess CO2. Drop an air stone (attached to an air pump) in it and see what happens.
I don't think you'll have a problem. I always wash stuff in vinegar. It's a great cheap and safe cleaner.
http://www.reefkeeping.com/issues/2004-09/rhf/index.php