I think the answer to your question is... "yes". Velvet is certainly more deadly than ich. But even if that is ich, it is not just a spot here or there. I would assume velvet, because the treatment protocol is the same. Read up on ich/velvet treatment and fallow periods in the disease forum. Of course, if you become confident that it is only ich, and you can tolerate occasional outbreaks like this, you can opt for "ich management" where you try to lessen the severity of outbreaks. But there is no way to eliminate ich or velvet from your DT through "management".