Why isn't this mysterious state of hydrogen detectable in tests?

The page you link to is essentially a big list of links. Useless.

I am immediately suspicious of anyone who generates buzzwords to describe their theory. Heck, he even registered "hydrino" as a trademarked term.

I'm not saying he's wrong. I'm saying he walks like a duck, sounds like a duck, wears feathers and swims all day in a lake.