Drain the tank down about 50% and use two nets...one for "herding" and one for catching...another person helping can get frustrating if you dont coordinate maneuvers.
I have tried the 2 nets and it does work, but depending on the size of your tank and things you have laying around you can try this.
In my 55 gallon tank I would put a egg crate in the tank to dived it in half with about 1/8 free space on each side. Drain the tank 50%. Then just keep moving the crate over until the fish have no where to go. then just net them out.
The thing to do is to take off the hood, turn off the fish tank light and turn on the room light. Watch from over the tank and occasionally the target will swim into the middle, when it is there, snatch at it and most of the time you will catch it.
I have a 90g with a big glass piece across the middle. 2 Netting is kind of hard when you can't look down at the fish.
I think I'm going to try the egg crate method. Going to put these Rosy's in a 10g for the time being until I find them a home. Should have did it last week before the return policy ran out, but eh what are ya gona do?