I have different nets. I have a set I use for established tanks in which the fish were bred here, or have lived here a long time. They have no apparent running diseases, so I use those nets in all those tanks.
I have another set of nets I use for QT fish. Generally, QT here is lifelong. If I buy petshop fish, they are never combined with wild caughts, due to the probability of them bring diseases in. Farmed fish can have immunities to things a wild caught would never meet, and if you put them together, the better fish often dies.
I also have different coloured water change hoses. I use the same one for filling, but different ones for emptying.
I'm going to visit my pre-retirement big city haunts in a couple of weeks, and I am prepping space and equipment. I'm going to be visiting two dealers in wild caught, uncommon to rare species, so I won't have to worry about farmed fish problems. But one sells only South American fish, and the other should have a selection of my favourite African fish. So they'll have to be kept apart because if they do carry anything, it'll be different from continent to continent. Disease exposure is a key concept to me - a first contact with what can be an ordinary disease in one place isn't just a human problem.
With luck, I'll have a couple of Corydoras species, and a variety of Congolese and Nigerian killies, Cichlids and gouramis/anabantoids. It won't be trusting luck that'll make me have nets(and tanks) for all, separate.
