Having trouble with temperature in incubator
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First thing to do: make sure you're calm. A temporary temperature drop is not nearly as bad as a temp spike. When you're calm, you can avoid making hasty temperature adjustments on the fly.
Second: are you relying on the incubator's built in thermometer, or do you have several additional thermometers inside? The built-in thermometers on foam incubators are notoriously inaccurate. Always always use an analog thermometer along with a digital.
Third: I've found that messing too much with humidity in foam incubators has a tendency to create temperature swings. I like to hatch "dry' (you can search any number of informative threads on this incubating technique, or talk to BYC user @AmyLynn2374), in other words, don't add any water until day 18 unless the humidity goes below 20 percent, and bump the humidity up to 70-75% on day 18-19. You would also monitor the air cells when candling.
Fourth: You can SLOWLY adjust the temperature up, and allow it to stabilize between adjustments. This is important to prevent a temp spike which could be deadly.
Hope this helps! You can also join several informative threads on here to talk with hatchers more experienced than me :) Good luck with your hatch!