Incubation lessons learned

Hatching chicks can be exciting and frustrating all at the same time. My first try was with shipped eggs. None hatched. Only one even looked like it had a chance. I found my incubator fluctuated quite a bit and it was hard to keep the humidity between 35-40 like the instructions I found said to do. After that I found that if I wrapped my turner arm in a paper towel the humidity levels were better. I also added a bunch of large rocks from our backyard as heat sinks to try to keep the temp stable. I also moved the whole thing to our front room.
My next try was with 27 local eggs. They were 5 days old at the oldest and only had to deal with a couple car trips, no shipping. Over the first 18 days we lost a total of 11 eggs. 2 had cracks so they weren't a surprise, a couple clears, and the rest blood rings at different stages. On day 16 I had what I thought were 18 good ones but by day 18 it was only the 16. We are on day 21 and we've had 8 hatch. The chicks are all doing well and appear healthy. The last 8 haven't pipped yet. I am losing hope that they will.
I'm glad I kept a spreadsheet of temp and humidity readings 3x/day. It helps me look back and see what might have gone wrong. 8/27 eggs isn't a good hatch rate. My temps averaged 99.9 with a spike one morning of 102.4 and a low of 98.1. I'm not sure if the spike was a real one or not though. I found the water in my fake egg was low. After I filled it back up the temps came back down. So it may have been reading a weird temp as the water was low. My humidity averaged 28% before lockdown. It usually fluctuated between 17 in the morning to 35 in the evening (after adding some water in the morning).
That all looks pretty good to me. After reading about common symptoms in incubation (great site for this) I found a common thread in the problems I'm seeing... low ventilation. I have 4 small holes in the top of my bator for ventilation, plus I thought the hole around my turner arm would work too, but I didn't add any more holes to compensate for plugging that one up. It didn't help that one of my fans (the one I broke during installation) broke around day 11-12 and the remaining one stopped working around day 14.
So next batch (I already have the eggs for it) I'm going to change a few things.
1) I'm going to drill more holes around the top for ventilation
2) I'm going to add the new fan (salvaged from a broken laptop)
3) I'm going to add an entire layer of rocks on the bottom as heat sinks (I boil these first!)
4) I'm going to close off the ventilation holes for the first 3 days like I saw to do on one article.
5) I'm going to rotate the eggs once a week to ensure they aren't sitting in a hot or cool spot too long. I used 3 temps at one point to measure temps at different spots but 2 were measuring the air and the third was measuring inside an egg filled with water so it's hard to compare. The air ones said 100 deg though so I think that was ok.

We'll see how the next one goes!