A sediment pre-filter sits on the main line ahead of the softener and catches sand, silt, and loose rust before they reach the resin bed and the control valve. It is a separate decision from the softener itself. Some homes need one and some do not, and the answer depends on what your water carries and whether the softener's manual calls for one. Work through three questions in order: does the water need it, can the plumbing take it, and who will change the cartridge. Only after those answers should you decide who does the install.
Start with the manual and the water
Open the softener's installation manual or the seller's written spec sheet and look for any requirement for a pre-filter or a sediment rating. Some units are built to expect one. If the manual is silent, ask the maker or the installer what sediment level the unit was rated for and whether your supply meets it. Well water and older pipes tend to make the case for a pre-filter stronger than a clean municipal supply does, but that depends on your source, so get the answer in writing rather than guessing.
Trace the pipe before you buy a housing
Follow the line from where water enters the house to the softener's inlet, and note what you find. Write down the pipe material, since copper, PEX, CPVC, and galvanized steel each call for different tools and skills. Note the fitting type at each joint, whether compression, push-fit, threaded, or soldered. Check whether there are shutoff valves before and after the softener, because a filter you cannot isolate is a flood waiting to happen when you change the cartridge. Measure the open space for the housing and the wrench room around it, and make sure the spot stays dry and reachable for a yearly look. Confirm the flow arrow on the housing matches the direction water moves in your line.
Decide by the pipe work, not by enthusiasm
You can usually handle the install yourself if you have working shutoffs, push-fit or compression fittings, a straight run of pipe, and room for the housing in a dry, reachable spot. Those jobs need a pipe cutter, a wrench, and patience with the housing seals. Lubricate the O-rings only with the lubricant the housing maker names, and test under pressure before you walk away.
Hire it out when the line is galvanized and needs cutting or threading you are not set up for, when you have to solder in a tight space, when there is no shutoff on either side, or when the run goes through a wall you do not want to open. Also hire out if your local building office requires an inspection or a licensed installer for the work. Rules vary from place to place, so call the local office and ask before you start. Our Missouri Water Softener Buyer's Guide covers the install order if you want to see how the pre-filter fits into the full job.
Settle who changes the cartridge
A pre-filter only works while its cartridge is fresh, and a clogged one starves the softener of flow. Get the replacement interval from the filter maker's own printed guidance, not from a guess. If the housing has a gauge, learn what a rising reading looks like on your gauge and write down the number that means change it now. Name the person who will do the change, buy the spare cartridges, and keep a simple log by the housing that records each swap. A pre-filter that nobody owns becomes the part that fails quietly.
What to ask a hired installer
Ask who pulls any permit and whether it is included in the bid. Ask what fittings the crew will use on each joint and whether they will test under pressure before they leave. Ask whether the existing shutoffs will be checked or replaced, and who covers the joints if one weeps later. Ask who changes the cartridge after the install, and whether that visit is included or billed separately. Compare those answers across bids, because the cartridge schedule matters as much as the first day's install.