I have a tank next to my water softner that the old owner said needs to be replenished with Calcite from time to time. On top of the fiberglass tank is an autotrol 1550-TC. I have disconnected tthe pipes and drain attached to the unit and now want to remove the top (control head?) to pour in the Calcite. It does not want to budge. Do I need to release the pressure?? if so how? If not any ideas on how to remove the top?