I think I've seen this before. I brought home some sick irridescent cats (with a bad case of ick) and treated them for the ick alone. Over the next week or so one of them developed the same "white line" apprearance as the clown loach in the picture. I was told my the LFS that it could be a secondary infection or it could be a slime coating that the fish is developing to heal (though I personally doubt the second suggestion they gave me ). Till this day I still don't know what might have caused it or what it exactly was for that matter. Scaleless fish are definitely difficult to treat sometimes. Sounds to me that you're going the right route with the treatment you've decided to go on though. I would go with a dose of anti fungal medication (well half dose or less). Hope that things work out for you.