Non-ActiveRecord based model being passed as string?

When ERB compiles your view, the result is a string. If I remember
correctly, the to_s method is invoked on objects, which in this case
results in the string that you are seeing. You need to pass in an
identifier that can be used to look up the specific instance of
HsdPair, or alternatively, use a low cost db like sqlite and pass in
the id.