Well what I mean by breaking down each input species is let's say the inputs to one of our unit ops consists of two species (an oxide and a mineral) and a given quantity of water. In order to specify the basis in mg/Kg we know the mg/Kg of each species and the amount of water but need to specify the basis in terms of mg/Kg of the basis species that the oxide and mineral are composed of, no? Since we know the mole weights of each basis species we can prorate the original densities to each basis species include H2O which is already a basis species and then sum? At that point we can specify the basis and run the go command to obtain our outputs. Is this not the correct approach? Thanks for any add'l insight.