How to replace a pool filter

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Introduction

Is your pool water staying cloudy even after running your pump for hours? Does your filter constantly leak, clog, or fail to maintain pressure? If so, it might be time to replace your pool filter. In this step-by-step guide, you’ll learn exactly how to remove your old filter, install a new one, and restore powerful, effective filtration to your swimming pool.

Why Replacing a Pool Filter Matters

Your pool filter plays a crucial role in keeping your water clean, clear, and safe. Over time, even the best filters wear out due to:

  • Mineral buildup
  • Cracked housings or manifolds
  • Degraded internal components
  • Reduced efficiency due to age

A worn-out filter leads to:

  • Cloudy or dirty water
  • Algae growth
  • Pump strain or overheating
  • Poor chemical distribution

Replacing your filter helps restore water quality, improves circulation, and extends the life of your entire pool system.

Step-by-Step Guide to Replacing a Pool Filter

Step 1: Choose the Right Replacement Filter

There are three main types of pool filters:

  • Sand Filters – Low maintenance, lasts 5–7 years, best for general use.
  • Cartridge Filters – Easy to maintain, efficient for smaller debris, no backwashing.
  • Diatomaceous Earth (DE) Filters – Best filtration quality, more maintenance required.

When selecting a replacement:

  • Match the filter type and size (GPM/gallons per minute) to your pool and pump.
  • Check that the inlet/outlet ports align with your current plumbing or prepare to adjust the piping.

Pool Owner Tip: If your current filter was undersized, upgrade to a larger one to improve efficiency and reduce maintenance.

Step 2: Gather Tools and Supplies

You’ll need:

  • Wrenches or channel locks
  • PVC pipe, fittings, and glue (if replumbing)
  • Teflon tape or thread sealant
  • Screwdriver and/or socket set
  • Replacement unions (if not already installed)
  • New filter (sand, cartridge, or DE)

Safety Tip: If you’re replacing an old DE filter, wear a mask and gloves when handling the grids or DE powder.

Step 3: Turn Off the Pump and Power

Before working on any pool equipment:

  • Shut off the pump at the switch or circuit breaker.
  • Turn off the timer (if applicable).
  • Close all valves on the suction and return lines to prevent water flow.

Step 4: Drain and Disconnect the Old Filter

  1. Open the air relief valve (if present) to release pressure.
  2. Remove the drain plug at the bottom of the filter tank to drain out remaining water.
  3. Disconnect all plumbing connections (inlet/outlet unions or pipes).
  4. Unbolt or unclip the filter base or mounting brackets.

Once fully disconnected, carefully remove the old filter from the equipment pad.

Caution: Filters can be heavy—especially sand filters. Use proper lifting technique or get help.

Step 5: Clean and Prepare the Area

Wipe down the pad or equipment area and remove any debris. Check for levelness and stability before placing the new filter. If the new filter base is a different size or shape, you may need to adjust the setup.

Step 6: Position the New Filter

Place the new filter on the equipment pad and align it so that the inlet and outlet ports line up as closely as possible with your existing plumbing.

Pool Owner Tip: Install union fittings on both ports for easier future maintenance and replacement.

Step 7: Connect the Plumbing

Use PVC pipes, elbows, and adapters as needed. Steps:

  1. Dry-fit the piping first to ensure proper alignment.
  2. Use PVC primer and glue to permanently secure each connection.
  3. Apply Teflon tape or thread sealant on threaded fittings.
  4. Tighten all unions and clamps snugly but don’t overtighten.

Wait 15–30 minutes for glue to cure before starting the pump.

Step 8: Fill with Media (If Needed)

  • Sand Filter: Add the required amount of filter-grade pool sand or glass media (use a funnel to avoid getting sand in the center standpipe).
  • DE Filter: Fill with water, then add the required amount of DE powder through the skimmer once the system is running.
  • Cartridge Filter: Insert the new cartridge(s) into the housing and close the lid tightly.

Follow the manufacturer’s manual for exact media or cartridge installation instructions.

Step 9: Prime the Pump and Start the System

  1. Make sure your pump is primed with water (see our guide on how to prime a pool pump).
  2. Open all valves and remove any plugs.
  3. Turn on the pump at the breaker or control panel.
  4. Watch for leaks, strange noises, or air bubbles in the system.

Step 10: Open the Air Relief Valve

Let trapped air escape from the top of the filter by opening the air relief valve. Close it once a steady stream of water appears.

Step 11: Monitor and Test

Run the system for at least 30–60 minutes, then:

  • Check for proper water flow at the return jets.
  • Check filter pressure on the gauge (record your system’s clean pressure baseline).
  • Inspect for leaks or drips at unions and valves.

Over the next few days, monitor your filter pressure and water clarity to confirm proper installation.

Common Mistakes to Avoid

  1. Using the Wrong Size Filter: Undersized filters lead to poor performance and constant cleaning.
  2. Skipping Union Fittings: Makes future maintenance far more difficult.
  3. Improper Plumbing Angles: Poor alignment causes stress on pipes and leaks.
  4. Forgetting to Prime the Pump: Can cause pump burnout or airlock.
  5. Not Checking for Leaks: A few minutes of inspection can save hours of repairs.

Extra Tips & Pool Hacks

  • Label Your Valves and Piping: It makes future service easier.
  • Clean or Backwash on Schedule: Follow a maintenance routine based on your filter type.
  • Keep a Spare Cartridge on Hand: For quick swaps during busy swim seasons.
  • Upgrade to a Multiport Valve (If Possible): Adds backwash, rinse, and waste functions for better maintenance flexibility.

Want to know when to clean your filter? Check out our guide on [how to backwash a sand filter] or [how to clean a cartridge filter].

Conclusion

Replacing a pool filter may seem like a big task, but with the right tools, clear instructions, and attention to detail, it’s completely manageable—even for DIY pool owners. A new filter brings better water quality, improved circulation, and less daily maintenance. It’s one of the best upgrades you can make for your pool system.

✅ Bookmark this guide and use it as your reference when you’re ready to upgrade your filtration system!