Nitrites are definitely no good. I'd recommend a water change asap. Even a perfectly healthy anemone can't tolerate ammonia or nitrites. What water do you use, tap or rodi? I can't say that I've heard of those lights, but my guess is the nem isn't getting enough.
Is that as open as the nem gets? Are the tentacles always that short?(really short tentacles typically mean starvation). It's hard for me to tell.. Is that the mouth gaping open? If that's the case, it may honestly be in your best interest to get it out of your tank. That anemone doesn't look too hot. If it does perish, your tank could go downhill fast. A nem can easily nuke a tank and its inhabitants.
I apologize for being blunt, and I'm certainly not trying to be rude. I know from experience that your best chance of success for keeping an anemone is to get the water quality up, go through the initial algae blooms, get some stronger lighting(metal halides, high output t5s, or a higher quality led setup), add some kind of intermittent water movement, and a protein skimmer. I'd also browse the anemone/clownfish section of the forum and read up on how to give yourself the best chance to keep one. I myself almost lost everything when my first died because I didn't read up enough on them. I didn't provide a very good habitat for it and it nearly cost me ALL of my livestock.