Goldfish are often oblivious to raking themselves against objects in the tank. Make sure that all surfaces in your tank are smooth. Run your fingers over everything in there. Same situation happened to our goldfish and it drove us crazy until we found out that our oranda was getting abrasions from the edge of a plastic cave.
I've never heard of silverhead sharks. Pics please? What species are these loaches and plecos? Please do remember goldies are coldwater while the rest of the fish appear to be tropical. Temperature and temperament become your top issues here.
I first thought they were Minnows but the lfs said that these are sliverhead sharks, although its hard to belive no one never heard of it. They dont do anything to the others, just swim very swiftly.