Here is a link to a thread about using vinegar to lower ph.

I have not tried it yet, but it does make sense. I couldn't find out the ph of the local water so I didn't go forward.

Here is a link that might be useful: Vinegar and cactus, is this true?

There's a lot of good info in the above thread. I use an injector to add citric acid to my tap water, but white vinegar is commonly used by those dosing manually. The amount used depends entirely on the alkalinity of your tap water. My tap water has an alkalinity of just over 300ppm CaCO3, so I have to use quite a bit of acid. People with very low alkalinity tap water, or those using rain water don't have to add any. Also, if using an organic acid like vinegar or citric acid, I wouldn't recommend leaving the acidified water sitting for long periods. The carbon in organic acids is a food source for bacteria. I get cloudy water if I let it sit overnight, so I always empty my watering can when done.

You can get an accurate pH measure of your water by using a pH test sold for aquariums. Use the drops-type tests not the dip cards. The drop-type is more accurate.

Keep in mind that aquarium pH test kits have a limited range. Many start at 6.0 or higher. The ideal pH endpoint is 5.8, as that is when all alkalinity has been neutralized. So just make sure you get a test kit that covers your desired endpoint.

Thanks for the feed back.