Like mentioned above what your seeing is quite normal and really nothing to worry about, but if you want to remove it just get an old credit card or drivers license and slide it straight down the front of the glass. This should remove the algae growth without disturbing the sand bed too much. GL.
I'm not sure if a wrasse in a 34 gallon tank is the best solution. Some of those worms might be bigger than that wrasse itself. And that mouth that they have, unless they can swallow the whole thing it should take some doing to kill it and then eat the remains. Hmm... Still leaning towards...
While limiting the food source will work, this can take quite awhile before you see any results. For a quick fix you could just lure them out into the open with a piece of shrimp on a hook and then siphon them out one by one. You might want to turn the lights & the the powerheads off when you...
Did the polyps just up and disappear overnight or was there still some tissue attached to the skeleton? The polyps may have just bailed out, in which case they're probably lodged in the rocks somewhere. If you can you might want to post a picture of your tank and list the parameters.
Those Koralia 425 pumps definitely leave something to be desired when it comes dow to GPH IME. I'd definitely get another one or perhaps two and position them somewhere in your tank so that the top of the water is quite turbulent. A far as a skimmer goes one that skims the surface of the water...