I am so paranoid I keep 3 thermometers in the bator. I had 4 for a while but really....! I don't think you can tell about temps from candling, but you will know if your eggs are developing and when they are not. Usually
I am sorry it worked out this way. Candling is an art I believe, and it takes time and experience. I am still trying to get it right. It'll go better next time.