All of the fish i have listed will be fine with Danios and all can be kept in a 30G for life.
Rainbow cichlids are a peaceful cichlid that might even be timid if there is no cover in the tank.
A single Firemouth would also be fine, Zebra Danios are ideal dithers for these.
SAPs would be much more of a challenge but IMO would be fine as they are only suitable for setups that contain other highly active species.
Most Apisto cacatuoide are tank bred so ph and hardness that they live in in the wild is irrelevant,
Also most of the uk has a fairly high ph
Thanks for the response. Certainly some food for thought there.
I found Apisto cacatuoide at my lfs yesterday, along with Bolivian Rams. However, these were being kept in pH 6.5 - 7.0 (even though they are in the same hard water area as me). Would it be possible to slowly acclimitise them to 7.8? I understand that Bolivians find 7.8 acceptable, but if the Apisto cacatuoide have always been in those conditions, I guess they would not be able to make the transition?
Will also do some serious thinking on the SAPs (no idea why I was typing 'SAFs' in my previous reply). Very keen on the species but did not want a species only tank. Would be interesting to mix them with the danios.