From time to time, on my bigger fish only 10"ish, I've seen small white specs moving. they are present with planeria in the tank but look different. the fish are mildly irritated, dashing aganst rocks and sand and flickering thier fins. I dont know if its a form of planeria or another bug of sorts. I've dosed the tank with potassium permangenant and they still come back after a few days. I've never seen any fatalities from this but it's annoying to say the least. If you think about the small closed system we keep these pets in it's a wonder we don't have regular major problems. I do larger more frequent water changes now than what I used to, so I don't see it as much now.
I don't know if that helps, just sharing my observations.