Need help! Introducing new ducklings to other ducklings (couple weeks old)

[leighton3]

I have 4 chicks (ages 7 weeks to 4 weeks old) and 3 ducklings (about 3-4 weeks old) in a large pool all together, got all of them at about the same time they are used to each other and fine with one another. Yesterday I got 2 new ducklings, one is a couple weeks old, the other is days-1 week old. The 2 are fine together. When I got home and put the two new ducklings in with the others, they were fine but but older ducklings soon began attacking the new ones. I created a new box and used chicken wire for the sides. I put the new box inside of the pool so all of them are together but the older ducks can not get to the new ones to peck at them. Is there anything else I can do? Did I do the right thing? Does anyone know how long it will take for my ducks to get used to the new ones? The chicks are fine and couldn't are less about the new ducklings. Need advice!! Thank you