An indexable cartridge and method that is useable in either a stagnant fluid environment or in a moving fluid environment with the indexable cartridge floatable in a stagnant fluid environment and securable in a moving fluid environment with the indexable cartridge having a housing having one or more diffusion ports and a sleeve having one or more diffusion ports indexable to a diffusion port alignment through resilient yielding of the sleeve while a set of ribs inhibit lateral flow therebetween.