Vinager to lower PH

First--why do you want to lower your pH? Where is it now, and where do you want it? What's the hardness(GH and KH)?

While my own grasp of this process is pretty basic, adding any acid--vinegar being one that's easily available--will eat through the buffering agents in your tank--the KH particularly--this won't always result in a stable water condition. You will need to treat the water for each water change, and you'll need to constantly test your conditions to ensure stability.

However--there are few reasons to lower most pH's. Most fish will be just fine in a variety of differing waters, as long as they are stable.

Another option is to find fish that more closely match the water you have. As orion girl says, making water quality changes can result in a lot of hard work and potential crashes.

I have used vinegar up until recently. I have added 1tsp to 10g. I keep discus in my tank among other fish. I had problem with one of them going on a rampage, couple of times a day. There was something in the water that was making them skittish. I have planted tanks and pressurized co2 injection controlled by a controller. I don't think it was vinegar, rather probably too much co2 or not enough nutrients in the water. I have increased the ph through co2 injection, added more nutrients to the water(discus essentials), increased the temp by 1F, and stopped using vinegar to lower ph in the holding tank on water changes. The discus looks like he's coming around now and hasn't gone on a rampage in 4 days - knock on the wood. From the look of it, my water was pretty stable as far as ph is concerned, otherwise the co2 injection would be on all the time.

Falcon