If the midas isn't grazing much then you may not have as much potential for competition with another blenny.
Hair algae is a pain! Lowering phosphates and nutrients in general will keep the algal growth down, and is often a better solution than adding another herbivore. Lots of fishes are touted as being the cure all for algae, but this rarely a reality. If I remember correctly, some species of rabbitfish will graze on hair algae, but this is a random thought (plus they have poisonous spines).
If you can, tackle the patches of algae with a toothbrush/wire brush out of the tank and give them a good rinse in tank water before returning to the DT. This is a pain, but you can scrub the rock much more thoroughly than any fish can.