Well... another one dead today. No symptoms, no other fish affected... time to save for another UV I guess
Im sorry to hear this.
Do you think there is a possibility of cross-contamination from the other tank where you had so many losses?
If the deaths have stopped in the other tank since you put in the UV sterilizer and there is a chance of cross-contamination to this tank than it points pretty positively to parasites.
But, also, with UV sterilizers they do cut down on the bacterial load in the aquarium ( help control mild cases --- where internal damage has not yet set in--- of bacterial infection from columnaris and aeromonas , for example). Cutting down on the bacterial load, the UV sterilizer allows the fish's immune system to manage a mild infection as long as there are no other environmental stressors to push the fish over the edge.
Anyways, I think that the decision to get a sterilizer on this tank as well is a good one.