Hello excellent aquascapers, I have a question about rocks. I recently placed four large local river rocks into my tank after doing the test with vinegar to make sure they would not react swiftly to acids, and they seem to be fine- only now my pH is creeping upwards (still safe, but it has climbed from 6.8 to 7.8 pH) I believe from the look of them and our local geology that the rocks are most likely basalt. Any ideas? I do like the smooth rounded contour and dark color, I can't find anything in the local shops rocks that are not striped, pink or orange, translucent, jagged/flaky, or have a cute little hole in the middle for the fish to swim through. If anyone is from the Seattle area, that is where I am prospecting for stones. These ones came from near Stevens Pass. Thanks!! P.P.