Get those tiny dry flies out, the fish are smutting! If you are faced with those tricky, dimpling rises to apparently nothing, then there's a good chance they are either taking tiny midge rf quite possibly terrestrials. Tiny beetles, ants or aphids are a definite choice and it's worth offering the fish something smaller to tempt them.
Fishing tiny flies may not be fill everyone with joy, but they really do work. I am finding success using Varivas hooks - sizes #27, #28 and #30 all have a place. Don't worry - even the fine wire hooks will hold!
CDC is useful for suspending these tiny offerings, but a pattern sunken will also work well, watching the leader for takes. Those surface bsed offerings should be in the surface film.