I am NOT (I wonder if I could type that word even bigger?) a chemist...
there are people on this list far better educated about how water and
everything therein "work." Having said that, I don't think peat buffers
in any way useful to an aquarist (ducking and running...?).
Your post this afternoon said that the pH was 6.3; that of this evening
said it was slowly rising, you had added pH Down, and it is now 5.5.
Thing one: if you have peat in water with almost no hardness, you either