Any incubator needs to be cleaned after use. Some stain doesn’t hurt. The risk comes from leaving stuff in there that microbes can grow in and infest the eggs.
Humidity is something with any incubator you have to get right. The professionals using the incubators that hold 60,000 eggs at a time have learned that it has to be tweaked to get maximum hatch rate. Different incubators do best with different humidity rates and where they are located or the time of year may make a difference too. Even if one of those commercial incubators is just moved to a different part of the same room they have to relearn it to get the best hatch rates. Different temperatures and moisture levels in the air at the intake can make a difference, maybe because of the location of the room air vents. They tweak the incubators by opening the unhatched eggs. You can look through these troubleshooting articles to try to understand what may be going wrong with the incubation but it is not always easy to figure out what went wrong. With eggs developing to the pip stage but not pipping it could be too high or too low humidity during incubation, too high or too low average incubating temperature, improper turning, lack of good fresh air ventilation, and I’m sure things I’ve forgotten. In general if the egg stops developing in the first week of incubation it’s because of something that happened before the egg went into the incubator. If they stop developing during the last week it’s generally something to do with incubation. Nor always, but generally.
Mississippi State Incubation Troubleshooting
http://msucares.com/poultry/reproductions/trouble.html
Illinois Incubation troubleshooting
http://urbanext.illinois.edu/eggs/res24-00.html
Dirty eggs can be a problem in any incubator. So can handling the eggs if you get them dirty, such as having dirty, wet, or oily hands. You might remove some of that protective layer of bloom that helps stop bacteria from going in through the porous shell or you may introduce bacteria from dirty hands. Always wash and dry your hands before handling the eggs. The problem is that if microbes get inside the eggs they will grow whether there is a developing chick in there or not. They will kill any developing chick and can really make a mess with the rotten egg smell or even leak or explode. I don’t know how bad that smell was but if it had a rotten egg smell this might have something to do with it. If it is just a light unpleasant smell, probably not.
Temperature is an important variable. Too high and the chicks can be malformed or even cooked. They can be way early too. If the average incubation temperature is too low they can be late or the chicks can be fairly big and mushy, not strong enough to hatch. Too high a humidity can do this too. As long as you don’t get too extreme for very long a temperature drop or peak isn’t always a death knell. The eggs are a lot denser than air so it takes a long time for the interior of the egg to change significantly and the eggs are pretty tough to that kind of variation. Still, variations in the internal egg temperature are not good, whether when storing the eggs before incubation starts or after incubation starts. A steady internal egg temperature is a good thing. One good thing about temperature and humidity is that you don’t have to be spot on to get a decent hatch. There is a fairly wide range of humidity and temperature where you can do OK, but the closer you are to ideal the better off you are. This range is why I’m not convinced humidity is your real problem, temperature possible but not necessarily so.
Not all eggs are identical either. Some have different porosity, different eggs may have different consistencies of the egg white (some are thicker than others), some may have lost more humidity during storage, sometimes relative size can have an effect. What may be a perfect temperature and humidity for one egg may not be all that good for another. You cannot be perfect for every egg, you have to try to find that balance that works for most of the eggs.
Any decent incubator, whether foam or other, has pretty good insulation. They need to be used right, things like setting them up where there is not a lot of outside temperature change, breezes or sunlight hitting them, putting the lids back on correctly, and opening the vents. There are some studies that show poor air exchange is actually good for the eggs during the first week of incubation, but after that they need fresh air. The developing chick inside is a living animal and needs to breathe in oxygen and get rid of excess carbon dioxide. The egg shells are porous so oxygen can come in and carbon dioxide can go out. Before it internal pips that exchange is through its blood but after it internal pips it is through direct breathing. The plugs need to be out. A forced air is set up to redistribute the air that is in the incubator already but should also bring in fresh air through the vents, but a still air with the plugs out should do a decent job. If you still had the plugs in, this is one that is could be a cause of your problems.
Some incubators are lemons, that can happen with about anything you get; cars, blenders, or incubators. Some are harder to use than others, whether that involves tweaking or how much you need to monitor them. You need to calibrate any instruments you use, thermometers or hygrometers, to assure you are getting good readings. That’s a real common problem on this forum, instruments don’t work right. If you read the instructions that came with the incubator, you should see a statement to not try to hatch expensive eggs the first time. That’s because a lot of them do need tweaking or you need to go through a learning curve to get things right.
You don’t have to open all the eggs that did not hatch, but opening the eggs to see what went wrong is how the professionals tweak their incubators to maximize hatch rates. They want to know what may have gone wrong before the egg went into the incubator or what went wrong after it went into the incubator. A normal hatch rate for eggs they put in their incubators is about 90%. Half the problems normally come about because of something that happened before incubation started and about half after incubation started. If they have 6,000 unhatched eggs they won’t open all of them, but they will do a representative sample. If they don’t how do they know what to correct?
With the air cells about the right size I’m not too concerned about your humidities. From your post the air cells were at the top of the eggs when they were in the incubator so you probably did not incubate them upside down. That can lead to really bad hatches, often but not always total failures. Your temperatures may have been too low. Maybe you can get a clue to that from looking at the unhatched chicks. If the yolk is not absorbed or they are underdeveloped that may be a cause. The smell you mentioned bothers me some, but I’d think poor ventilation as a possible cause. It could be something totally different. It’s really hard to tell from this side of the internet.
The guy that had five of your eggs and only one hatched pretty late, how did the other eggs he had in with them perform? Were they late as well? Did he open your eggs to see if they even developed? I’ve had extremely poor hatches from eggs I got from someone near here when I brought them home on a really rough country without good padding, but those eggs never even started to develop. Handling may have played a part in your four, though I’d like to know how other eggs did in that incubation.
I am really sorry you did not get any to hatch. That’s especially hard when you have a young child involved.
