Checkerboard cichlids. Get a small group of 6 of them to start with then when 2 pair sell the other 4. If not a Trio (1 male, 2 females) of any type of Apistogramma would be fine, i personally would go for Apistogramma agassizii.
Almond leaves are good for lowering the Ph as well but in a small tank with internal filters peat is pretty manageable
The Hongsloi are quite a small species so would work pretty well if you find a local source where they have been bred in tap water that would be good for you as you could keep the young in the tap water but if you get wild maybe look into the peat and almond leaves.