Amavi
Fish Fanatic
Vietnamese loaches will be fine in a 180l .
As far as "sharks" go; you could try some true sae (Crossocheilus oblongus). But they are borderline (if you are very conservative with stocking) as far as size and activity goes.
pH is really not that big a factor with most tank bred fish as they have usually been in non acidic water for generations. In any case, most people report keeping even fish such as captive bred discus at slightly basic pH levels with no problem. Problems arise if only with egg development, but adult fish usually don't mind most specific pH levels, as long as extremes and rapid fluctuations are avoided.
Ah I have been told so many times they will need to move so I organised my brothers tank. I will be happy to keep them as they are funny to watch. The female is guarded some bog wood at the moment poor corys have to live in the ship with the male!
I forgot to add I have a type of pleco I have no idea what type he is but hes no bigger than 8cm