Last night I was just casually checking the PH in my new tank so it's ready for fish on monday. Well it showed up as 8.4!!! I imedietly went and test the tap water 6.8. I thought it must be the gravel so got a sample of the gravel and did the viniger test, No bubbles not one. This tank is going to be a angels, tetras, corys tank so I dont really want it to be that high. The tank has been sitting empty for about a week. Does anyone know what could have caused this? How do I lower it with out adding chemicals or putting a hell of alot of driftwood in it?