The Yellow N2 cartridges are the same inside. They do not have the little tabs that keep them from falling down into the plumbing on a HotSpring spa.
If you want to use the yellow ones, you have to use the little extension sticks that come with them. You stick 'em on the cartridge and break off enough so you can close the filter cap, but still get the things out in four months.
DO NOT leave them in longer than four months.
