A little advice that might improve your results....
Pulverize about half the dri-ice.
(inside a few folds of newsprint, hit the ice block through the paper with a hammer...or the heel of your boot. This is an easy way to pulverize the dri ice.)
Pour the pulverized half of dri ice in with the chunk half of dri ice.
Then pour the water into the container with the Chunk and the pulverized ice.
The Pluverized dri ice has more surface area...and this acts as a catalyst to speed the reaction...releasing more CO2 initially.
Then the Chunk of dri ice will react more slowly and will continue to keep the CO2 levels in the appropriate density range....until the feeder rodents succumb.
CO2 is a fairly effiecient and humane way to euthanize the rodents....provided you keep the density in the proper range long enough to effectivly kill the rodents.
However, it is not as effective (especially at killing PINKY rats/mice) when the concentration of CO2 is less dense.
Pinky size feeders can go for longer periods of time in an anoxic state....(without oxygen).
They sometimes will require larger ammounts of pulverized dri ice....added to the water mid-way through the initial reaction.
Chunk Dri ice also often forms a shield or barrier of regular ice (frozen water) around itself when partially submerged in liquid water....slowing or sometimes even stopping the reaction. Fully submerging the dri ice usually solves this problem.
Hope that helps.
Harlin Wall - WALL TO WALL REPTILES!
970-245-7611