First time hatching help in DIY incubator HELP

I was laid up from surgery complications for a few months and used my time to research and build an incubator.

While I've been around farming all of my life this is our first flock and first time to incubate eggs.

We incubated 4 dozen eggs of mixed breeds (cheap eggs) they started hatching a few hours before day 20. 28 eggs hatched during the 24 eggs before getting to day 21. Presently starting day 22 the other 20 eggs have not done anything.

I'm not sure if I have enough posts to post picture of my incubator for reference. Here is a brief description of what I've built:

Plywood box insulated with 2" styraoam walls covered with FRP board for easy cleaning. Lower chamber has a heat sink of 6 gallons of water in two tubs, rocks, 3 100 watt halogen bulbs, there is a computer fan to push air into this chamber and finally all of this is covered by an aluminum plate with a 1" air circulation space on the outside. Above this are two double cake pans that have water added in during lockdown to raise the humidity. Finally the egg chamber with egg turner, 2 computer fans on the lid to keep air circulating and temp distribution.

When I set it up it ran for a couple of weeks before adding eggs. I put some water balloons in and measured temp with a human mercury thermometer. With my thermostat at 100.3, I got a consistent reading 99.5.

Considering hatching was happening before day 20 and seems to have finished right at day 21. Does this mean that my temp was a little to high?

Also the only hygrometer is a cheap analog on the end of an outdoor thermometer. When I added water on day 18, I was getting a reading of 50-55.

 

I might add that loud chirping can be heard from some of the I unhatched eggs. I'm thinking that I may need to try lowering the temp by a small amount and find a way to raise the humidity by placing sponges in the cake pans with water to increase surface area.

 

As soon as I posted the last post, I thought of sponges and have placed some in there. We will see what happens. With these I'm presently registering 70%.

While I probably have some temperature differences I tried to design the bator to minimize this. Air flows up from the bottom on the outside and out through a vent in the center with two computer fans centered on thirds pushing air back down.

We started with 56 eggs then down to 48 for ones that didn't develop. When I candled at lockdown the airspace looked like diagrams that I've seen and was uniform from egg to egg.

 

Thanks for the replies. Since putting sponges in, we do have some more eggs starting to hatch.

I'll put sponges down in the cake pans next time.