Removing large threaded ring on my jacuzzi/carver cartridge filter

[kevreh]

There’s a large high strength plastic ring that holds the top onto my cartridge filter, it screws on. Part 7 below. About 24” diameter. Once it’s on there for a while it’s hard to unscrew. There were 4 tabs on the bottom of the ring I would hit with a mallet, 3 have broken off. The ring has some indented circles on the top, looks like some kind of tool fits in them (spinner wrench?) Whats the right way to loosen the ring?

Reference diagram;

 

[kimkats]

Bump for more eyes

 

[kevreh]

Thanks for the bump. Maybe this is why I got such a good deal on it, I miss the stainless spring loaded bolt on my old Pentair DE filter.