PH down Using vinegar.

I used Apple Vinegar into my 1gal water tank. I PH'd to 5.8 by 10 drops of vinegar. Next day, I checked the PH again nd it came out 8.2 (which is higher then tap water) lol.. Why is it keep changing? .. I am using aerogarden. thanks.

Go to an aquarium shop and get some pH adjuster (Up and Down) and some BUFFERING solution. If you don't buffer the pH to where you want it, you will always get erratic swings. The directions are on the bottles, and are pretty straight forward. Don't worry, it will be safe for plants and your smoke.
It's a lot easier to maintain proper pH in soil than Hydroponics.

http://www.ehow.com/video_4801918_buffer-solution-work_.html
http://chemwiki.ucdavis.edu/Physical_Chemistry/Acids_and_Bases/Buffer/How_Does_A_Buffer_Maintain_Ph%3F