Hey reefwars, thanks for the interest in helping me get to the bottom of this. To be honest I haven't done a ton of troubleshooting. I've been in the new house for a year, and after getting the tank moved in (and sump plumbed into the garage) it's been on autopilot for the most part. Top off the freshwater, occasional checks of Calc and Alk, feeding fish etc. minimal water changes, probably not maintaining the skimmer as well as it should be. I had a diatom outbreak at one point (cloudy water) so I picked up a UV sterilizer and ran that for a month or so, cleared it up and no problems with that since. Trying to learn more about RO/DI systems and the consequences of old filters is part of that troubleshooting
To answer your other question, yeah between being temporarily setup at my mom's house (between selling the condo and moving into this house) and now the nuisance algae situation the corals are definitely suffering unfortunately.