I don't like being involved in disease threads as there can be more confusion with different methods. @Colin_T asked for some info in an earlier post, I will not counter anything he says here. Heat is normally the safest treatment (and I concur with others about surface disturbance), but from the photo and your description you may lose the loach, so be prepared; ich is far advanced. And I also agree, do not change filter media; rinse it in a bucket of tank water but don't replace it.
Am I correct in assuming you only have the one clown loach? If yes, do not get any more when this is resolved, as this fish must have a group and it gets very large, up to 12 inches/30 cm. If the one you have has been alone (no other clown loaches) that is one very likely cause of severe stress, and that brings on disease.
Am I correct in assuming you only have the one clown loach? If yes, do not get any more when this is resolved, as this fish must have a group and it gets very large, up to 12 inches/30 cm. If the one you have has been alone (no other clown loaches) that is one very likely cause of severe stress, and that brings on disease.