Ah, another quest for purple fish! Unfortunately there really aren't any; only emperor tetras, which are too big, purple pencilfish, which are rare and horribly expensive or the occasional betta.
The higher pH might be a problem for most tetras; cherry barbs and shrimps perhaps? A trio of shelldwellers (although you'd have to ask the shellies about tank size, they're not a fish I've ever kept)?
Go for a nice Betta, create a flooded plain/rice paddy biotope for it. Still water, nice clean sand and heavily planted. Maybe some White cloud mountain minnows if the temperature is on the lower side.