In the Pet Warehouse catalog they have the Dupla check valve (page 68, $14.50) and a brass check valve (page 23, $1.90). Does any one know if the brass valve is all brass or does it just have a brass casing? And if it is Co2 safe? I know the it's only a difference of 12 buck but with the initial cost for setting up a planted tank (my first) every dollar counts. tia jim