You might consider using meifan stones.
Actually, last Saturday I bought some meifan stones and the resulting tea tasted bad, stale like, afterwards I brewed the same tea without stone treated water to make sure it wasn't the tea leafs that were stale. The test proved that the stones were the culprit.
Can you tell me how you prepared your meifan stones before using? I boiled them for 20/30 minutes. and left them in a pitcher with my distilled water. For the first brew the water was left for 5 mins, and the second use was after an overnight soak. What do you think, was the water left too long in with the meifan? Have you had any problems?