The lime build-up I was referring to was from your water source. Hard water has a lot of lime in it, so if you spilled some water and let it evaporate, you'd see this white residue left behind. I'm no water expert, but with a starting ph of 8.0, it could be all the lime making it that high, or then something else. Anyways I don't think you'll have a problem, I had white residue on my soil before (from hard water).