Its fine to keep an anemone in a 12 gal nano, I have a green bulb anenome with a cinnimon clown hosting and they are excellent. But you must upgrade the lighting to a retro-fit kit, no less than 36 watts for the 12 gal nano. I retro fitted mine with 65 watts of Power compacts. My own custom design. Also you must watch you water perameters closely. They have to be right on. I do 10% water changes every 5 days. the deluxe nano is better than the standard first gen set up which had only 24 watts which isnt enough lighting. And also, do not put an anemone in the 12 gal until it is stable and has been matured for at least 9 months. Let it age for awhile. Get coraline algae to grow etc. first. be patient and have fun. It is no walk in the park for nano's. They are intended for the semi experienced to experienced reefers. But anyone can do one. This is my opinion, and some people have good sucess, while others kill everything because they dont pay attention and they dont listen to reason. Bigger tanks are more stable and less likely to crash. ie 55 gal or larger. They are more for the beginers, but the cost is higher but are more forgiving in making mistakes, Nano's are less forgiving in a mistake and what you do happens right now, there is no going back to correct the mistake, but when in dought do a water change, it might save you. This isnt to scare anyone, but all must be aware of nanos. Have fun.