Pentair Triton II TR100 Sand Filter

Either there is a secret to this or I am simply not as strong as I used to be.  I want to remove the filter closure using the Closure Wrench that came with the filter, however, I cannot make it budge.  I have released the pressure via the air relief valve but still nothing.  Is there another secret I do not know about or do I contact a younger person to do this for me?

Thank you for any advice you may give.