Thank you, Monty and Cuttlegirl for taking initiative! You rock! I couldn't help but take the opportunity to post "OMG". Cuttlegirl your information has helped some of my overthinking, with the H2O motion and O2 questions. I was thinking of floating smaller containers in a shallow tank, but I hadn't thought as small as petri dishes. Did you keep only one animal per dish? Also, I wasn't sure if the smaller containers should have a small piece of fine mesh on the bottom for H2O exchange with the larger tank or if they should each be closed systems?