Acetic Acid is Vinegar. It does NOT work. It will drop the PH for a short time but then it will go back up. Use a different kind of acid.

ya Kevin I used to use vinegar too and it does'nt keep ph in check for very long I now use ph down for aquarium tanks .So if you have a pet store near by that will solve your problem.I have a ph of 6.6 to start with and after I add my nutrients and 4-5 drops of ph down per gallon I'm very close to where I want to be.The little 4 oz bottle (that I bought for I think 6 or 7 dollars)will last me a very long time so I hope this helps a little.

It will take a while for the ph to be adjusted, vinegar will work. If you had ph down it would do the same thing.
Happy growing. ( i suggest letting your reservoir grow a LITTLE algae, that will keep your ph in check)