Lots of people use a 65watt clip on light from Home Depot or Lowes to light their fuges. If you get a fist sized ball of chaetomorpha, it will grow extremely fast under most conditions.

You might want to check out http://www.melevsreef.com/fuge_bulb.html for info on fuge lighting.

Also, I hate to say it, but you're success in raising a mandarin in a 45 gallon tank is going to be limited. I've seen report of people with 125+ gallon tanks that had trouble keeping them alive. You might want to check out these two threads on here before purchasing one.

http://www.maast.org/index.php?name=...ic&t=22408
http://www.maast.org/index.php?name=...ic&t=22045

Good luck with it -