What kind of test kit are you using? Did you try again? It's possible it was a false reading. Have you tested your tap water (or whatever source water you use)?
If you don't have any fish in there, you don't have any ammonia in there (obviously). Which also means your "seeded" bacteria will only last so long. Ammonia is basic, it will raise the pH. I would test your tap water (let it sit for 24 hours before doing so). If your tap water is at 7.6, something is off. If it's closer to the 6.4 you're reading in your new tank, everything is fine and it will probably shift as it begins to get established.