You will need MH for that anemone. But, you're gonna find out that it's gonna outgrow a 45g before you know it. You are planning your next tank right now already, right?
This is a picture of my >24" ritteri in my 72g. Some would argue that the 72g is way too small for this animal as well, and I would agree ... but it's more of a dedicated setup buying me time until I can build a bigger system myself. (Which is coming soon now that I have the space for it!)
They get to well over 30" eventually. Better start planning for it. Incidentally, mine went from 5" to 20" in about 3 months. I've had it for over three years now.