Why are my chicks dying on day 20 before pipping?

It is very simple to hutch chickens eggs. (Home made incubator) i adjust the temperature, that was quite rough cause i had to make adjustments while i was incubating eggs. First clutch of eggs hatched 1 day early (lost most of them), so i just decrease little very little the temperature. For humidity i don't have a hydrometer i have a glass of water in my incubator. at day 18 when i stop turning the eggs i open up the incubator when i see too match moisture dripping in there 1 time the day make it work for me. Moister goes away when i hand turning my eggs moister increases as i don't open the incubator, simple. I have see many videos and tutorial to put large plates with water under the eggs, the humidity in some of them is way too hi the eggs are fool of moisture, Never saw a broody chicken wet her eggs. For me my hatching rate is 100%, except if i have an infertile egg, You must clean your hands every time you handle the eggs clean the incubator and for gods shake don't increase your humidity to much. If you starting to see water drops in the incubator the humidity is TOO HIGH, i have try with commercial incubators and none of my thermometer or hygrometer output the same values. Anyway i think that you losing the chicks because of a virus or the low nutrition of the eggs. I' m in day 19 this time, i have in my incubator some eggs too small that don't have the criteria for getting them incubate. I post some pictures again in Monday or Tuesday with my new chicks. I have 19 eggs but 2 was not fertile so know i have 17.

8 of 17 hatched at night and keep going one little guy hatched 2 days early and have not absorbed all the yolk sack.. What i do is tide with string the yolk sack to prevent bleeding and cut it of, works for me. Also put iodide where the cut was made, feed them with boiled egg for get them nutrition. Still have 4 eggs that they have not piped but they will probably until tomorrow and 5 more that they hatching right know. The good news for me is that the smallest eggs hatched perfect without any problems. I did have an egg that piped the wrong way but it hatched as always normal without help.

New here, and new to chickens! But I've been studying up a lot to ensure I don't lose any to my own ignorance! One of the things I've heard is that it is better to incubate one clutch at a time. Not to have eggs of different due dates, because they will have different humidity needs at different times. Maybe that's why?

True it is best to put your eggs all together, i hand turning my egg and when i count at day 18 i just want to stop messing up with the eggs. Other reason is that when they hatch they make a lot of mess in there you don't want to have open eggs and even blood and still run the incubator for more days waiting for other eggs to hutch and of course you can handle better the chicks when they are at same age. When i start my first incubator i have only 7 eggs cause i try to measure my temperature and each thermometer gave me a different value. My best was the simplest mercury thermometer i have, the digital thermometers gave me 40 Celsius witch is not true. Same with the hydrometer. Better to have lower temperature rather than higher. Higher temperature will surely kill the embryo. And even if you loose some chicks you must know that there other reasons of some eggs won't hatching even baby chicks die. Most of them are bacteria in the incubator virus in eggs and low vitamins in the eggs. I am waiting for all of my eggs to hatch still there 3 more to go. Those 3 have not even pipped but i give them full day 22 and even day 23 if needed without disturbing them, also when you candle at day 5 or 6 or 7 when you find a clear egg get it out if it gets rotten probably will other eggs get bad.

What if you chicks pip internally but then never pip the shell and die? I had 6 internally pip then die. What am I doing so wrong?

My cat ate my only chick to even hatch. It can't get any worse.....

Could it be from too little ventilation? The older the embryo grows the move oxygen it takes through the pores of the egg. Or too much humidity?

I would guess the humidity may be to high and when the chicks internally pip they are drowning from the moisture condensation in the air cell. This is what I do.

To calibrate a hygrometer you will need:

1/2 cup table salt
approximately 1/4 cup water
coffee cup
hygrometer
large resealable freezer bag

Place 1/2 cup of salt in the coffee cup, and add the water. Stir for a bit to totally saturate the salt. The salt won't dissolve in this amount of water; instead, the salt should have the consistency of wet sand.

Carefully place the cup containing the salt/water mix in a resealable plastic bag. Place the hygrometer in the bag, away from the cup of salt and water. Note: make sure none of the salt/water mix comes in direct contact with the hygrometer, or the hygrometer may be damaged. Completely seal the bag.

Place the sealed bag aside at room temperature for 8-12 hours. Pick a location free of drafts, out of direct sunlight, and away from heating or cooling vents. The temperature should be fairly constant.

After being in the sealed bag for 8-12 hours, check the reading of the hygrometer. It is best to read it while still in the bag, since if your house air is dry the reading may go down quickly once you take the hygrometer out of the bag.

The relative humidity in the sealed bag with the salt/water mix should be 75 percent.

If yours is the adjustable type, adjust the screw or setting so that it would have read 75 percent. You will have to do this very quickly, or remember how much you need to adjust the setting (e.g. for mine, it read 72 percent when it should have been 75 percent, so I would need to set it ahead by 3 percentage points). You may want to put the hygrometer back in the bag for another 8 hours to double check your adjustment.

If yours is not adjustable (like mine), simply make a note of how "off" your hygrometer reads. If it reads below 75 percent, you will need to add the difference to your actual readings. If your hygrometer read above 75 percent on the calibration, you will need to subtract the difference from your actual reading. Here are some examples to help:
Case 1: after sitting in the bag for calibration, my hygrometer read 72 percent. It should have read 75 percent, so the difference is 3 percent. I will now add 3 percent to the readings I take on the hygrometer (e.g. in a tank) to get the actual relative humidity.
Case 2: after calibrating in the bag, a hygrometer read 80 percent. It should have read 75 percent, a difference of 5 percent. I would have to subtract 5 percent from readings when using the hygrometer to get an accurate relative humidity.

Remember: always give a hygrometer about 2 hours to stabilize before taking a reading, as changes in the relative humidity may take a while to register accurately on a hygrometer.