Use housing wrenches to remove standard, commercial, and Max Flow housings.  The Double Wrench also fits residential RO Membrane Housing caps.  Housings should be hand tightened.  If they require more than 1/4 to 1/2 of a turn with a wrench, consider removing, cleaning, lubricating, and reinstalling the housing oring.  If the problem persists, replace the oring.  Orings should be lubricated with food grade silicone grease at every filter change.