OK I admit I am relatively new at this, but I do have a successful hatch under my belt, AND I just candled my day ten eggs and they're all looking great so far (I had to chuck one at day 7 because it was clear).
First, make sure your parent birds are getting absolutely prime nutrition. If you can let them free range (and I know not everyone can) they should be getting loads of new spring greens and bugs/ worms to eat. The healthier the parents are, the healthier the chicks/ducklings. Make sure they have access to calcium (oyster shell free choice, or whatever) so the egg shells are nice and sturdy to keep out bacteria.
Second, As everyone else has said DO NOT TRUST the thermometer/hygrometer built in to your unit. Get a second and third opinion. Calibrate your separate hygrometer by doing a salt test (Put salt in a small cup. Add water until it's a consistency like mud. Place the cup in a plastic zip seal bag with the hygrometer sitting next to it - NOT in it - then seal the bag walk away for 6 hours. When you come back, if it doesn't read 75% mark how many percentage points off it was + or -, so you will know what the actual reading is). A separate hygrometer does not have to cost a fortune, I got mine off Amazon for ten bucks and it works perfectly.
Leave the incubator set up and running for a full 24 hours before you put ANYTHING in it. And by set up and running I mean consistently staying at the temp you want it for that full time. If you run the incubator for 24 hours and it's at 105 half the time and 94 for several hours, and then 99 degrees the last half hour... it's not ready yet.
Third, Carefully collect eggs from your birds. Gently brush off dirt, but do not wash or scrub them. Store them wide end up in paper egg cartons. Either turn them several times a day, OR place one end of the egg carton elevated, and switch which end is elevated 3-4 times a day. Do not store any longer than 10-12 days before incubating. Do not refrigerate. DO NOT place in the incubator on different days or try to incubate different species in the same batch until you have more experience. Just don't do it. You need to get the feel for how your incubator works best first before trying to do stuff like that. While it may be tempting to pack the incubator full in hopes that something will work, keep in mind there are benefits and drawbacks to each scenario: full incubator or small-batch. Decide what you can live with and go from there. I started with a small batch, and I'm working on a bigger one this time now that I've seen how my incubator works.
Fourth, Look up different photos of candling eggs. Realize that there's a wide variation in what's normal, and egg shell thickness/color will affect how much you can see. Commit to not throwing any eggs away unless they smell and are clearly bad. This will prevent situations where a viable egg is mistakenly destroyed.
For circulated air incubation, you want to shoot for 99.5 or so temp, and humidity seems to do best between 30-40%, but monitor your air cells and adjust as needed.
These are just the thoughts I had as I was reading your story. I feel for you, as you seem frustrated. I hope you will soon get to experience the thrill of watching a new little feathery friend hatch, it's amazing, and worth the wait!
