So based on a bit of googling I've decided I have hydroids on my glass.
^not a pic of my tank but very similar.
In any case, everything I've read seems to say these guys are harmless, but they also seem to say it's related to a new tank. That part interests me since my tank is about 2 years old at this point. The only recent change was the switch over to RODI. Any opinions on if that would effect these guys?
your initial photo is something I have seen multiple times in reef aquariums. I would just wipe them down.
I've never heard of a hydroid problem, and I assume in a mixed reef/garden variety reef they probably don't present a major problem.
I am going to assume here so take it for what its worth, but unless you are keeping acropora/sps, or you unless you see a lot of them, they probably aren't terrible. If you have an sps heavy tank, yeah, maybe you need to eliminate large colonies.
they also need nutrients so... I dunno if that helps, good luck