Unfortunately, the Blue Tang's minimum tank size is 125 gallons
. Some will say the Yellow would be ok in a 90g, and others will say a 125g is best. Madarins need a large population of copepods to survive, so before you need to get one, you need lots of live rock, and you need to begin a pod population. This is best done with a refugium, but it can be done withought. Have with your tank!