The Pentek Big Blue housing lasts for years; Pentek recommends replacing the plastic sump every 10 years. The 5 micron cartridge needs changing about every 4 to 6 months on a typical well, up to 12 months on a clean well and every other month on a dirty one. Lower water flow at the taps means it is due. If you are changing it more often than every other month, call Aidan before buying more cartridges: a spin-down screen or a backwashing sediment tank may be the better fix.

The 20 inch Big Blue housing is about 23 inches tall and 7.5 inches across, with 1 inch NPT ports, and takes standard 4.5 x 20 inch cartridges. Leave room below it to lower the sump at cartridge changes. The 20 inch cartridge is twice the length of the 10 inch, so it holds more dirt between changes. For 1 or 2 people, the 10 inch Big Blue kit ($165) is enough; for 3 or more people, this 20 inch kit.

About every 4 to 6 months on a typical well. It depends on how much sediment your well makes: on a clean well a cartridge can go 12 months, on a dirty one every other month. The sign is a drop in water flow at the taps. Our 5 micron 20 inch replacement cartridge is $55; Aidan says a 5 micron cartridge bought locally averages about $25.

5 micron, the cartridge that comes in the kit. Aidan uses 5 micron melt-blown cartridges in every Big Blue: it catches sand, silt and rust without slowing your flow. He does not recommend moving to a 20 or 50 micron cartridge to make it last longer, because the finer sediment then goes on to your treatment tanks. If a 5 micron cartridge clogs within weeks, call Aidan: a spin-down screen or a backwashing sediment tank handles a heavy load better. Our micron ratings guide explains the choice.

No. Aidan recommends replacing the cartridge when it becomes dirty rather than washing and reusing it. If you are going through cartridges quickly, a reusable spin-down screen or a backwashing sediment tank may fit your well better; call or text Aidan and he will tell you which.

On the main line right after the pressure tank, before any treatment tank: well pump, pressure tank, this Big Blue, then the treatment tanks. Nothing goes between the pump and the pressure tank. With both an acid neutralizer and an iron filter, Aidan sets their order from your water test. If you also use a spin-down screen, it goes after the treatment tanks to catch any media they let past. The Big Blue goes first because sand and grit wear valve seals and foul the media in every tank behind it.

The 20 inch cartridge is twice the length of the 10 inch, so it holds more dirt between changes, and the housing does not slow your flow. Aidan's rule: for 1 or 2 people, the 10 inch Big Blue ($165) is enough; for 3 or more people, get the 20 inch. Both have 1 inch ports, the same 4.5 inch cartridge diameter, and a 5 micron cartridge in the kit.

Very little when the cartridge is clean: Pentek rates the empty 1 inch housing at a 1 PSI drop at 15 GPM, and Aidan picks the 20 inch because it does not slow your flow. As the cartridge loads with sediment the drop grows, and lower flow at the taps is the sign to change it. Shut-off valves on both sides of the filter make the change quick.