Just tapwater and prime mate. I did think about getting an HMA filter, but with everything going as it is there's not much point really is there? I don't really want to start messing around with RO though.
I was told I may have trouble getting the discus eggs to hatch in my tap water, it may be too hard at around ph7. The breeder I bought the first discus from just used treated tap water, not sure what the ph is around Birmingham though. TBH I'm not going all out to breed them anyway, I just see it as a sign that they're happy. If I do get some wrigglers then that's a bonus