Wait a minute kare21162, when you swapped the tops the temperature kept dropping? Are you sure that you don't have a battery going bad in your thermometer or something? If the top on the chicken incubator is working ok then it should work just as well on the bottom of the duck incubator, right? That's got me confused, or either it's the strawberry parfait I had for dessert at lunch.
If all else fails, see if you can stick the duck eggs in with the chicken eggs.
Best wishes,
Ed

If all else fails, see if you can stick the duck eggs in with the chicken eggs.
Best wishes,
Ed