I have a Culligan Mark 89 that is over 20 years old. I've had ALOT of trouble with water pressure for the past 4 years. When you first turn on water anywhere in the house it has great pressure, but within a few seconds it goes to nothing. You cannot have water running in two places at the same time. I recently changed the regen on the softener to every night and cleaned out the salt tank, but this hasn't helped. Any ideas?