Welcome to our forum.
I have a caldera spa. Do you perfer the Baqua Spa or the Monarch Silver Cartridge?
The silver cartridge with some chlorine (don't belive it if they say you can go chlorine free) is the way I go and it's works great.
I got the Monarch today. My caldera filter compartment has like a 2" pvc pipe that sticks up and the filter slides over that. The only way the monarch cartdridge will fit is if I stick it in the tube.. It wont stay in the filter long enough to slide the filter onto the 2" pip sticking up. I hope it doesnt block the suction.. anyone have a 2004 Caldera Niagra?