I feed mine ghost shrimp that are fed and loaded with a lot of nutritious food. They are finicky eaters when you first get them. You want to make sure you can get them ghost shrimp. If you want some links to ghost shrimp, email me.
Ry84@MSN.com is the email.
I would not recommend putting one into a heavily stocked 20, but one that does not have any fish would be fine in my opinion. You do not want the little guy crowded.
Lighting does not matter. Actually, since lions are nocturnal, they do not like very bright lights, so regular lights are fine.
Yes, you definitely need a skimmer. All saltwater tanks need one in order to remain healthy longterm. Plus, they add a ton of oxygen to your water.
If you do not view the lion eat anything in the store, DO NOT BUY HIM! Don't let the LFS feed them feeder fish for you, this is very bad for them. If they cannot feed em ghost shrimp of frozen, do not buy him. Many lions are thought to be caught with cyanide, and if the customer continues to buy this, this practice will continue to go on. Be smart, and make sure the lion definitely eats in the store before you buy him.