Lemon peel

Hey there new to forum, and new to a 75 gallon tank,I need some help, I think I made a mistake, the tank is been running for about 4 weeks , there is a clown fish that I introduce 2 weeks ago and doing fine, parameters are good, the question is that I got this lemon peel angel last Sunday, and is refusing to eat anything I trow at it, and its developing some brown spots along his dorsal fin and body, any suggestion, did I get it to soon? will it thrive?

Thanks in advance.