Thanks! I haven't owned a blue acara either, but I just want a blue fish in my tank for variety. So far, I have one gold severum (yellow), one blood red parrot (orange-red), one leopard ctenopoma (brown and black), one fire eel (red, blown and black), 3 tinfoil bars (silver) and 5 loaches (well, we all know what color they are on the loach forums ). I just thought a jet black fish and a blue fish would finish my collection off.
As long as the acara has adequate territorial boundaries, like most cichlids, they leave their tankmates alone. A 180g isn't that bad for both acara and loaches living together. No problem with BGK. You just have to make sure the loaches are adequately sized enough not to end up being eaten by their tankmates.