from what i've heard, they're just like all the other pods in ur tank. if u see one of them, there are plenty more. just keep a close eye on all of ur fish and take it slow. isopods can be pretty small, so you'll have to routinely check on them. the most common time to see them is when the tank lights turn on in the morning. isopods are nocturnal, so if any are attached to fish you will momentarily see them jump off and go hide in the rocks. i wouldn't recommend adding any expensive fish. one thing that isopods are known for is attaching themselves to base of a fish's tongue. they detach the tongue and live there, acting as a parasite. i've seen a few small ones in my tank, and i've only seen one on a fish once. it was a tiny one attached to my firefish's tail. i like to think that my six-line and pseudochromis are taking care of the bigger ones, but i can never be sure. the only real fix to an isopod infestation is replacing all of your rock and sand.