How to get Hayward cartridge canister locking knob off?

swimcat

Well-known member
Aug 18, 2012
72
Bethpage (Long Island), NY
I just bought & installed the Hayward cartridge filter below. Hand tightened everything yesterday. Was hot and sunny today. Cartridge pressure was already high today & return flow was very slow. Already, I can't budge the locking knob on top of the cartridge canister. Any suggestions? Do I need a klorkinator or some other tool? Here's the equipment description. I'll update my profile asap - been trying to get into the pool for days but pool equipment was flying off the shelves here on Long Island, NY.