I have looked everywhere for dry ice locally and they either really don't have it or they're lying to me. I found this site ( http://www.alysion.org/euthanasia/ ) and wanted to try the method of putting a box inside of a garbage bag. I have about 20-25 5-6 week old rats to euthanize. I bought pet store rats and they popped out babies. I am unable to find any more homes and cannot keep them. I thought it would be more useful to be able to freeze them to feed our ball python. I don't want to spend much on it as I never plan to breed my rats and these were unplanned litters obviously. I want it to be humane, but the instructions seem to be for one animal and I don't want to mess this up. Do I need to increase/change the concentrations? Also, I have a ten gallon aquarium and found a method using that on http://www.ratfanclub.org/euth.html , but the same problem with the quantity of rats. I have a styrofoam cooler as well if there is some way to use it for this purpose. Thanks!