what is the difrence b/w a cavy dish
http://www.petfooddirect.com/store/p...3255-groupName
and a super pet one
http://www.petfooddirect.com/store/p...3257-groupName
also what are good sized diameter ones
a: For a 41q tub
b: For a 15q tub
c: For a 6 qt tub