Well, I just learned that ph "down" is not the same thing as the ph "decrease" I bought at the pet store when I bought my ph tester. Evidently, it is not good for plants. I've only corrected the ph with this for 2 waterings... maybe it won't kill anything. So, I guess I'll be using cider vinegar.

I have no idea how much to add, so I'll have to experiment. My tap water is in the high 7's or low 8's. My tester only goes to 7.6 and it is pegging that out. I'll post results.