I give an Ally's Shrimp is about size 6 or 8 a try on a long leader with a floating line. And I would use it in black or purple is the original range/red/black did not work. Also, I would tie it on a standard weight hook instead of a low-water hook to get it to sink between 4 inches and a foot below the surface.
Another possiblity is to use a dark colored Irish Shrimp style fly tied on a heavy size 6 or 8 hook. Again with a floating line and long leader. This should get you down, but not on the stones.
The third possiblity is to use an intermediate sink tip, short leader, and either of the above flies or a dark spey fly of about size 4 or 5. something like the Lady Caroline or Black King.
These just might work since the water is summer low' but the temperature is normal winter low. Seems like you need to get down, just not on the stones. And since the water is low and clear, a small darkish fly seems to be in order.