Headed out the door for the week in two minutes, so excuse grammar and to the point.
Throw away the swing arm and purchase a refractometer.
Single full siphon balanced will likely cause a flood at some point. What happens during a power outage?
Euphyllia does not look bad at this point.
What you called Xenia is actually probably Anthelia.
I would leave Money Plant / Halimeda to grow.
Biopellets provide food for bacteria that UV sterilizer kills… sell UV to someone with a pond or freshwater tank.
Pull chaetomorpha algae apart. Lack of iron may be slowing it down, but DO NOT add carbon as you could have a macro algae blue in the display.
Cut pellets down to minimum or none(if fish do not eat them) for time being.
Good luck, ttyl.