Just the thermometer that came with it. I have it elevated to almost the top of the eggs and adjust it slightly often keeping it closer to 100 than 99.It wouldn't necessarily kill them but it may delay them a bit. You could candle them to see what's going on but try not to move the egg to a different position to the one it's sitting in inside the incubator. See if the air cell has drawn down on one side or if you can see if any have internally pipped.
Do you have an independent thermometer? The temperature on the incubators are often incorrect, so an independent, calibrated thermometer is essential for ensuring your eggs are at the correct temperature. Here's an article on how to calibrate your thermometer and hygrometer: https://www.backyardchickens.com/ar...incubator-thermometers-and-hygrometers.73634/
Keep them in until day 26. Hopefully they are just being slow.
I tried candling but hardly know what I'm looking at so just put them back in and left them. I don't have a hygrometer but it has water trays as a guide. I used tray 1 for first 18 days then filled trays 1 and 2.
I have the same incubator but I DO NOT trust the hygrometer as it indicates 20 points lower than the independent calibrated hygrometer that I use. I also fill the first outer channel for the first 18 days of incubation which gives me about 30% humidity where I live, sometimes it goes up to 35% but no more. I then fill the next 2 channels for lockdown and this gives me good successful hatches.
