Hi guppie,
I don't have tetras. That's the only fish in your tank, right? But this is my opinion on distilled water. For right now, I would do your water changes with the distilled water. I say "for right now" because your ammonia is so high, and your pH is low -- from your last post it was 6.0. Ammonia becomes more toxic at higher pH levels. While you still need to get the ammonia down, at least your pH is low, and the ammonia is not as toxic to the fish. If you start raising your pH now, while the ammonia is high, that will harm the fish even more.
Distilled water is generally not good to use as the only water in your tank. There are no minerals in it that the fish need. I did do some searches on different kinds of tetras, and their preferred pH range is as low as 5.5 to 7 pH. I would say to get through the cycling first, then someone who has tetras can tell you how they handle the pH for them. Good luck!