The anemone looks great. The yellowish green color looks a lot like mine. I am not used to seeing so many folds in a merten's carpet. They usually lay a bit flatter.
Have you thought about putting a little shade cloth over your spa? The couple guys who grow corals outside around here have colored plastic and/or shade cloth over their tanks. Your anemone looks a little light in color. I wonder if that is because they normally occur in deeper water and the light in your spa is a little too bright.
I'm not saying that is what you should do. I am just saying that if I were in your situation, I would do some research to see if indeed merten's are a deeper water species and why do (as least some) outdoor coral farmers shade their containers a little. It might be worth a little internet surfing and a couple phone calls.
Your system looks awesome. I have thought about setting up a greenhouse tank myself. All I need is a little time, money, a way to get a big container into my backyard and oh yah..... a greenhouse.