Just a quick update, it seems that I might have the cyano on the run. I've just kept up with my weekly water changes and removed some of the crushed coral where the stringy slime was really clinging. Of course I always scrub the sides of the tank too to remove the few spots that it seems to like. Looks like it's not really coming back so far, but it's only been since Saturday.
Water params were the same as the last test, ammonia 0.0, nitrates 5.0, phosphates 0.0, ph was down to 7.8, calcium up to 440. All the corals and my one little fishy are happy and living the good life.
Keeping my fingers crossed.