First, how big is the tank? im going to assume its not the 46g.... cause if it is than that means you just made a big mistake, you purchased something for your tank on impulse. being impulsive is the quickest way out of this hobby, if you want to be successful then you need to read before you make ANY decision...it will save you money and heartache. how long has this tank been running? and like asked above what are the parameters and what kits did you use?
things you SHOULD know; hippos are ich magnets and are very shy at first. Naso tangs dont always adjust well to new tanks or captive life..also they can be difficult to get eating.
If you havent done so, read up one both of these fish! that is step number one when considering buy new livestock! fish from the sea arent going to forgive for not knowing their special requirements. I've had/have both of these fish (sold the hippo, the naso is still with me) so im pretty familiar with their behavior. hippo tangs can become very aggressive, and they grow FAST. Mine went from 2.5" to 4.5 in just 6 months. The naso will become very personable when it comes around, but its a very passive fish so no adding aggressive fish for some time..also they like to swim....A LOT...all night my naso swims from one end of the tank to another. Why? i dont know, but it just does, therefore ample swimming room is a must, i actually need to upgrade soon for that matter.
HTH,
David.