The Alpine Pure NSF Certified Gradient Density Prefilters have different micron size as the water travels through the cartridge. First cartridge 50-30-20 micron and the second 20-5-1 micron and NSF approved.
The replacement parts are 10 B PS GD 20 Gradient Density 20 micron. 10 B PS GD 01 Gradient Density 1 micron. Lamp is a S36RL and Quartz tube QS-012