Here across the pond (US) we have Cider Vinegar @ 5%, and white Distilled Vinegar @ 5%.
Distilled white vinegar would be the best (less organics) to try. Either of course, could cause bacterial blooms and the raw cider vinegar could seriously cause more serious blooms which could effect oxygen levels etc.
All our streight vinegars are made from fermented apple juice. I would not use flavored vinegars (as mentioned by Peter) as used in salads etc. either.
The acidity is Acetic acid which should be safe. It should also be stable in a tank but you should be cautioned to test often in your tank/tanks…until you are sure it reacts ok with your setup.
I did use vinegar years ago in some tanks and it worked. BUT I can’t remember why I stopped using it.
So, if you want to go ahead, with a PURE DISTILLED VINEGAR and of course GO WITH CAUTION.
I understand Peter’s concerns and they are valid, and I would only tell you to try it with the distilled version of vinegar, and again with no fancy flavored additives.