Just to add a little more info (
LOL can never have too much), make sure you provide plenty of hiding spaces, especially with a single loach. Loaches need some sort of cave (I use a natural one made by my driftwood, as they ignored the ceramic one I bought for em
LOL) to feel safe and comfortable.
Theres a good chance you won't see much of the loach. From what I've read of other's experiences (remember, I have 3, and I always have), a single clown tends to hide. You could not give him a place to hide to try to assure you'd see him. Thing is, you'll wind up with a VERY unhappy, unhealthy loach; its better to let him hide all the time then stressing him by not giving him a safe place, and he will likely not live very long in that case (stress = lowered immune system).
Lastly, I hope you QT him. Loaches, especially clowns, are wild caught and usually come in with all sorts of nasty parasites/diseases; usually ich. I QT all my loaches for 3 weeks, where my other fish usually get 2 weeks. Do keep a very close eye on em in any case. In the case of ich, it may appear soon because of the stress of all moves. Also, they may have internal parasites; white stringy poo or strange things hanging from its vent is a sign. There is also something called "skinny disease". Doesn't actually seem to be a parasite as it responds to antibiotics (let me know if you need to know what kind; I don't remember off the top of my head). With that one, they start to, well, get skinny and waste away.
Lastly, madasa makes some very good alternative suggestions. There are other loaches available which don't get as large and it would be easier to have a small school in your size tank; there are other fish with similar markings (not necessarily loaches,although I think loaches are awesome!). Not only do I have 3 clown loaches, I also have 3 yoyo loaches (one in the main tank, 2 new buddies for him in QT). They're silvery white with funky black markings; they're called yoyos cause those black markings look like YOYOYOYO...neat eh? Adult size for them is around 6 inches tops, and they are just as amusing and active as clowns.