Ah .. forgot to mention, but you just reminded me of something.
My ritteri HATES being moved! Everytime I've had to move it, where some handling is involved (impossible to avoid when you have a 24" anemone), it releases some kind of invisible fish death. Don't know if it nematocysts that sting a fish's gills, or just slime that coats their gills, but either way, non-clownfish fish suffocate to death.
Although I've seen a few smaller specimens, to me it seems that ritteri's get ridiculously large. I know the original poster said his tank is a 300g, so I didn't mention this, but I guess it bears mentioning to anyone else reading this thread to be prepared for their eventual size if you intend to consider this species. And to give you an idea how fast they can grow, mine grew from a paltry 5" at time-of-purchase to well over 18" within *about 2 months*. And it continued to grow beyond that as well. Craziness.