Make sure to keep an eye on your other 2 tanks. If he has something infections then you just contaminated both of them.
i think the infection was from the mollie tank i just picked 1 dead mollie and other is moving very slow so i think the oscar might have something the tank were i put him was fishless for a week or so it was my betta fry tank that i am not using anymore but i will use it to have an eye on the oscar for a few days if he can make it he still comes near when i am watching him but his slow movement worries