You can initially clean the tank with some soapy water. There is no need to use bleach or go crazy with it. I don't use bleach ever around my animals, but that is just a personal choice. Chlorhexidine is the way to go! http://reptilebasics.com/store/home.php?cat=249

I personally mix 4 oz or so per gallon rather than the 2oz recommended. It is extremely safe as a disinfectant.(its used as an oral rinse in surgeries)