Nassarius snails but zombie snails works just fine
It may just be the position of the powerheads relative to your rockwork creating deadspots. I can't tell for sure but it looks like you have a "stream" type powerhead in there. Wide flow patterns (like the koralia) create more random flow and help eliminate dead spots. Not trying to get you to run out and spend more money on pumps but too little flow and/or the wong type of flow will contribute to cyano growth. If the problem persists only in thos areas, changes are improved flow (along with nutrient control) will help.
If the cyano is mainly on dead coral skeletons that it sounds like it is being fueld by the decay on those skeletons. You have a HOB filter don't you? Grab a large bag of Chemipure Elite or some low ash carbon and some GFO (Rowaphos or Phosban) and throw the media in your filter.
FWIW, I have 1 hermit in my tank and I won't add anymore. May want to add back a few snails and possibly a florida fighting conch or two.