Hi Michelomal!
First of all, welcome to the fun and challenging world of incubation
I am at 5000 ft, not too far off from your situation. I don't think the altitude will be your problem, rather that you are new to the game and don't have experience with your incubator plus you are using shipped eggs. For me, I expect that my hatch rate will be very low from shipped eggs and am delighted with a 20% hatch rate. Not trying to be negative...just keeping it real!
More info about your incubator--brand, whether it has a fan, are you hand turning or have an autoturner, is it new, what type of wells for water does it have? Then more info about its location--does the room you are incubating in have a stable temp, have you checked its humidity?
I am concerned that you calibrated the hygrometers but they don't match each other--perhaps try calibrating at 99 degrees next time would give you better results. Well, got to move on from where you are this time around. IME, digital are not as accurate as analogues and usually read low by a lot. I have one that reads 16% when it should read 40%…yikes.
Anyway, there are many folks that even do dry hatches where they don't add any water until lockdown with great results. For me, I can add water most of the time because we are so arid here but have done dry hatches in the summer with the incubator in the basement because it's more humid down there. Not sure what your climate is like? I aim for 30-35% humidity during incubation and then try for at least 65% at lockdown.
Normally there is quite a draw down of the size of the air cell during incubation. Have you checked out pictures of what you should be seeing? I would rather see an air cell that is too large rather than one that is too small, in all honesty. The air cell is where the chick pips into first and it needs.some headroom to breathe.
For me, I started weighing all of my eggs prior to setting and writing the number in grams right on the shell and also in my log. For shipped eggs I also candle.the eggs looking for detached or ruptured air cells and draw a.line around the current air cell in pencil. I then reweigh the eggs when I candle at about 10 days. I am aiming for a minimum weight loss of 13% by lockdown and can figure out if I am in track and adjust the humidity if I am not--wanting see around 7-8% at this point. I have successfully hatched eggs with well over 20% loss at lockdown and have had more losses below 10%. For me, weighing works better because the shape of the egg can be deceiving--the pointier eggs will look like they have bigger air cells, rounder eggs smaller ones with the same weight loss.
If you feel that you are having trouble with the humidity being too low, especially at lockdown, I recommend that you put a humidifier in the room where the incubator is. Incubators draw in outside room air so if you start with higher humidity it's much easier to raise the humidity inside the incubator.
I suspect that your problem is the discord between the hygrometers and that is making you over think and fret over the eggies when everything is probably fine! Did you take any photos of your eggs when you candled them? If so you could post them so we can look at the relative size of the air cell with you.
Good luck!
