Damp sponge in a low dish right under the vent so you can drip more water on it?
I have the advance model with the humidity pump, so it adjusts for me automatically. Ruby has more tricks to help, hopefully she'll check in soon.
If it's the Brinsea Octo, I posted this pic earlier of how I do it with paper towels. Hope it helps:
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The paper towels act as a wick. Also make sure your lid is seated on tight!
Oh, like others mentioned, the shelf liner works great. I pre wash it alone and then toss it in a load of laundry. After 3 hatches, it still looks good as new.
Just wanted to mention that some people have a hard time getting lockdown humidity up in a Brinsea Octo, especially if you live in a dry climate or in the winter with a furnace running. I fill the wells, then put in a double layer of paper towels and push them into the wells, then fill them up...
It's a great system, and I do almost the same thing, but not as fancy. I have a door from the coop to the brooder box made out of chicken wire in a frame. After a few weeks, I pull up one corner, clip it open, and the littles can go in and out but the bigger ones can't follow. There's also a...
My daughter had a wonderful midwife that helped her through a tough delivery. So glad more Hospital OB departments are employing advanced practice nurses/ nurse midwives these days! Really worked well for her -had the attention of a midwife, but was in the hospital in case of an emergency...
I'm sure you could successfully incubate anything with a shell!
I was thinking more on the lines of a beginning hatcher with only one stable incubator. Not sure I'd recommend it for a first hatch, but I'm chicken-only so what do I know?
Maybe you'll go for five next year? Got any Emu?
One thing to think about - will the duck eggs and the chicken eggs lose moisture at the same rate? I've found that smaller, lighter eggs need more humidity, larger, darker eggs need less. So next year I'm going to try to only set similar eggs together in the same incubator so I can adjust...