If your TDS is reading 0, your water is fine.
Is the tank getting much natural light?
Remember you have to be FAR more tedious with the water in a QT than in the DT. And I will correct RCreations, Ammonia is certainly worse than Nitrite, but neither are good. I am by no means the QT expert, but when I add a fish to QT, I feed next to nothing for the first several days, a QT tank can't remove waste like a DT can. If you are having Ammonia I would do large water changes to get rid of it, and ALWAYS have water mixed and ready when you have your QT running.
I personally wouldn't do SPS in that tank, what are the total watts again? And how many times turnover per hour?