I use water crystals and have not had an issues, you don't let them eat it, just put it in a cup to help maintain the humidity.So it says water cyrstals on package and I look in garden. Is it made by miracle grow. My machines would spike on a gallon of water. I usually use the bottom of the incubator the top is usually so full of eggs. I do 44 at a time in incubator. So you put it in the distilled water you get at market and you add it with your sryringe or squirt bottle depends how much time I have on lock down. The other one I just pour a little squirt bottle of the water and pour it around the turning try's. I've tryed to use paper towels before but it would spike.so I stoped. I have rocks and penny's at the bottom of incubator . The humidy sponge was to replace the two sponges at bottom of the incubator . And maybe put one in the fence area of dog house. So if it got low I could help . It high in back and low in from in dog house on temp and humidity.