Quarentine is the best way I know to keep from introducing ICH or any other disease to an operating tank. Clown loaches like warmer temps so a good two weeks at about 80F temps should make sure they are "clean" of Ich. angels also like warmer temps so they are a good match temp wise.
although I would say a 40G tank isn't big enough to hold clowns for long. I have had clowns and angels together for many years and have no problems.
check this link out
http://www.fishlore.com/Forum/84-clo...consider.0.htm
carol