Need PH advice

As soil, i'm using one that originally had a ph 6.
Is this theory correct: If i'm watering the soil with a ph6 water, the soil it's self will have a ph6?

Moving on to a tricky question:
I'm having difficulties adjusting the ph of my water.
I'm using a 7ph water, and modifiy it by adding apple vinegar, untill I get a ph of approximately 6.
After i water my plants, they look great. But after a day or two, the leaves start to "melt", untill they end up in a downwards vertical position, and overall, the plants look awful.
After I feed them with a ph6 water, they rebecome vibrant in about an hour or two.
I know that the ph can change over time, but this is ridiculous, right?

Is it something i'm doing wrong?
Isn't water with a touch of apple vinegar a good technique to bring my water to the right ph for my plants?

I'm also in the process of recovering from a PH issue and I found my solution by capturing good old rain water which test out at PH 6.0 - 6.3. I was told not to obsess with the PH of my soil but to focus on the PH of the water I'm using. I'm not sure about the whole vinger thing but consider snagging some rain water the next time it rains, in door plants love the crap out of the stuff.

A picture would help. Sure you aren't just under-watering?

I think you're obsessing over pH a bit much, which is common. People like me are going to tell you that you probably don't have to fiddle with the pH of the water or your fertigation solution. Neutral water is perfectly fine, but after you add most nutrients\supplements or even a teaspoon or two of blackstrap molasses the pH will drop a bit... and it's no big deal.

Most of the time even within the range of 6.1 to 7.4 is perfectly acceptable. In fact, N-fixing bacteria do best with a pH slightly over 7. If anything don't worry so much about what is going in, just take note of what comes out (run-off pH).

Nullis is dead on. Don't obsess on PH, and test the runoff. It sounds like what would happen if you had a huge plant in a tiny pot. Or, the plant has been transplanted into its current container and hasn't (for some reason) rooted into the new medium. This is basically an underdeveloped root mass. I've experienced this with rockwool croutons. Maybe give us some more details on the soil, container, plant size, transplant history, a pic, and a bunch of other shit. I can pretty much tell you with confidence...it's not a PH issue.

also, could a mod change this thread's title(into "needing some general help", or something similar)?

if your soils is at 6 , I would water with 7, might even add some lime. really nothing to be overly concerned with.