Why Is My Pool Filter Blowing Out Sand?

A working pool filter is key to keeping your swimming pool water clean. But when your filter starts spitting sand into the water, you’ve got a problem.

In this article, I will give you tips on how to tell if your filter needs replacing, reasons why it is blowing out sand, and most importantly, how to fix the problem.


Main Takeaways

  • Shattered laterals can be one reason your pool filter is blowing out sand.
  • A second reason could be due to a broken seal. The most common seal to break is the O-ring.
  • If your pool filter is still blowing out sand after fixing the laterals and seals, it’s likely time for a new filter altogether.

Reasons Why Your Pool Filter is Blowing Out Sand

There are two potential reasons why your pool filter is blowing out sand and debris.

Reason 1: Shattered Laterals

If you find a layer of sand on the bottom of your pool floor, this is a surefire way to tell that your lateral is broken or cracked.

Several pipes formed the lateral, around 6-10 concentric pipes. These pipes help the filtered water from the sand bucket flow back into the pool. When the pipes break, including even the tiniest crack, the sand enters the pipes and gets carried back into the pool, resulting in murky, sandy water.

How To Fix It

You will need to completely replace the lateral in your pool filter. Simply patching up the cracks is not an option and will result in more damage down the line. Luckily, replacing the lateral is easy enough to do yourself. Here is a step-by-step guide on how to dismantle and replace the lateral.

Supplies Needed
  • Replacement lateral pipe
  • Filter sand
  • Teflon tape
  • Unions
  • Lubricant (optional)
Step one: Turn off the pool pump

Begin the process by turning off the pool pump. I recommend turning it off at the circuit breaker.

Step two: Drain water from the pool pump and disconnect the waste hose

Remove the cap from the pool pump to release the water out of the tank. Once the water has drained, disconnect the waste hose from the multiport valve.

Step three: Remove the multiport valve

To remove the multiport valve, unscrew the unions connecting to the Pump and Return ports. Be sure to keep the unions in a safe place, so they don’t get lost. You will need to unscrew all bolts and clamps to remove the multiport valve.

When removing it, use a gentle twisting motion to lift it out of the tank. Place it somewhere dry for safekeeping.

Step four: Tape the standpipe

A handy trick to stop sand from entering the standpipe while changing the sand is to tape the opening closed with teflon tape.

Step five: Remove sand from the tank

Carefully scoop out the sand in the tank so that the laterals are revealed. This will help when removing the laterals out of the tank.

Step six: Rotate and lift the laterals out of the tank

Gently rotate the laterals up to lay flat against the pipe and slowly lift the entire ensemble out of the tank.

Step seven: Replace the damaged lateral(s)

Any lateral that has cracks or holes needs to be replaced. Start by unscrewing the screws, pull the top section off the bottom section to free the laterals, and remove the broken lateral(s).

Place the new lateral on the bottom section, ensuring it’s in the correct position. Then place the top section over the bottom section. Tighten all screws so that both sections are pressed together.

Step eight: Clean the tank and check the laterals

Before placing the lateral ensemble back into the tank, check that all laterals can be rotated to fit into the tank opening and that you have cleaned the tank out of any debris and old sand.

Step nine: Place the laterals into tank

You can now place the laterals and standpipe back into the tank and rotate the laterals about 90° degrees into the correct position.

Step ten: Pour the sand back in the tank

Pour the sand into the tank until the laterals are all covered. Be sure to pour the sand in gently so that you don’t lift the laterals and standpipe. It is usually recommended to fill the filter about three-quarters of the way. Make sure to follow the manufacturer’s instructions if you are unsure. Most tanks will provide markings for correct sand levels.

Step eleven: Lubricate O-ring

A good idea is to lubricate the O-ring on the multiport valve to last longer.

Step twelve: Put the parts back together

Place all dismantled parts back together.

Step thirteen: Backwash

The final step is to do a quick backwash to ensure all the sandy water is removed from the pool and the filter is working correctly.

Now, there should no longer be any sand in your pool water.

Reason 2: Broken Seal

The sand filter has multiple rubber seals and washers that separate the filtered water from the sandy, dirty water. If your water looks cloudy and you notice sand in the pool, the seals might be broken or snapped. Since the seals work with chemical water, they can corrode quickly and break.

The seals can be found between the outlet, the inlet, and the standpipe.

How To Fix It

Fixing the seals is relatively easy. The pool tank will need to be dismantled and all the broken seals replaced. I have provided a handy step-by-step guide on how to do this.

The process is similar to the one to replace new laterals.

Supplies Needed
  • New seals and washers
  • Lubricant
  • Filter sand
Step 1: Turn off the pump

Be sure to turn off the pump at the circuit.

Step 2: Drain the water

You will need to drain all the water from the tank first by opening the cap.

Step 3: Dismantle all parts and check seals

Much like the process of replacing laterals, you will need to gently dismantle all parts of the filter like your waste hose, pump and return ports, and multiport valve. As you dismantle, inspect each piece with a seal or washer to ensure they’re not broken.

Step 4: Replace broken seals

Any seals that are cracked, snapped, or just look really old will need to be replaced. The most common seal to break is the O-ring found on the multiport valve. Remove the old seal by rolling it off and place the new one on by rolling it in. Use lubricant to make this process easier.

Step 5: Place sand back into the filter

Put new sand into your filter if it’s time to change out the sand. However, if your sand is just a year or two old, simply put the used sand back into the filter.

Step 6: Put the parts back together

Put all the dismantled parts back together.

Step 7: Backwash

Finally, perform a quick backwash and make sure everything is working properly.

By replacing all of the seals, your sand filter should now be working as it should be with no leaks.

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How To Tell If Your Sand Filter Needs Replacing

So, you’ve replaced the broken laterals and the snapped seals, but your pool water is still cloudy and full of sand. Unfortunately, this means that your sand filter is at the end of its life and needs to be replaced.

Another way to tell if your sand filter needs to be replaced is a noticeable decrease in efficiency despite frequent backwashing. If this still doesn’t convince you to get a new filter, a bad sand filter clogged with greasy, sandy “lard” certainly will.

Bottom Line

Broken laterals and snapped seals are the most common reasons your filter is blowing sand into your pool water. So the next time this happens, don’t panic, you now know what to look for and how to fix it. If the provided solutions don’t work, it is likely time to buy a new sand filter. Check out my guides on sand filter basics, common sand filter problems, and the best swimming pool filters for more information and recommendations.

Questions? Let me know.

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