Acceptable Humidity Range

The humidity level in my egg box dropped a bit today. It was 90% up until today. It dropped to 80%. I am sure it had to do with me airing the box out last night. So what is an acceptable humidity range? 80%-100%? At what percentage is a red flag to increase the humidity? Thanks.

u want to be as close to 100% as possible u can add a little water in the corner of the tub to raise it up

Put about 2 oz of water as suggested. Now I am at 95%. I'll just make sure that it doesn't dip below 90%. Thanks.