Shower filters do not have an absolute micron rating as they are not designed to filter out particulates or sediment only chemicals, in particular chlorine. I am not sure what certification you are referring to here. Perhaps you could explain this a little more for us.
We do have a bath filter however this involves removing the spout on the bath and screwing on the chrome 45013 shower filter with a spout attached. This system is not on the website, it has the part #45015 and a cost of $142.00.
Please let us know if we can be of further help.