Short answer
The most common cause is a cracked lateral or standpipe inside the filter, per Leslie’s and NH state pool filter guidance. Other causes: too much sand in the tank, a worn multiport valve gasket, the wrong (too fine) sand, or fines after a fresh fill, which a thorough backwash and rinse clears. A broken lateral means emptying the tank to replace it, not buying a whole filter.
Causes, most likely first
| Cause | Clue | Fix |
|---|---|---|
| Cracked lateral | Steady sand at the returns, worse after backwash | Empty the tank, replace the lateral |
| Broken standpipe or hub | Lots of sand, sometimes sudden | Empty the tank, replace the assembly |
| Too much sand | Sand level above the flange center | Remove sand to the label amount |
| Worn valve gasket | Small amounts, water at the waste line on FILTER | Replace the spider gasket or valve |
| Sand too fine | Play or all-purpose sand was used | Replace with #20 pool filter sand |
| Fines after a fill | Only right after changing sand | Backwash and rinse again |
Causes from Leslie’s troubleshooting guide and NH DES, which lists a broken under-drain lateral as the cause of sand in the pool.
How to check the laterals
Pump off, pressure off
Turn off the pump and breaker, and open the air relief until the gauge reads zero.
Drain and open the tank
Pull the drain plug, then remove the lid or the top-mount valve.
Dig down carefully
Scoop or vacuum the sand down to the laterals. Go slowly near the bottom; laterals crack easily.
Inspect each lateral
Look for cracks, broken tips and missing slots. Check the hub and the standpipe too.
Replace and refill
Swap damaged parts, half fill the tank with water, and pour the label amount of sand, mask on.
If you are emptying the tank anyway and the sand is a few years old, replace it: how to change pool filter sand. Use the label amount from the calculator, not more.
Preventing it next time
- Half fill with water before pouring. It cushions the laterals. Hayward’s manual calls for it.
- Confirm the laterals point down before pouring.
- Do not over-fill. Stop at the label amount.
- Turn the pump off before moving the valve to protect the gasket: valve settings.
Parts and tools
Questions people ask
Is a little sand in the pool after changing the sand normal?
A small amount right after a fill can be fine particles in the bag. Backwash and rinse thoroughly. If sand keeps coming back after that, a lateral may have cracked when the sand was poured.
How do I know if a lateral is broken?
Steady sand at the returns is the main sign. To confirm, drain the tank, remove the sand down to the laterals, and inspect each one for cracks or broken slots.
Is it sand or something else?
Rub it between your fingers. Sand is gritty and does not smear. Fine dirt from the yard and dead algae can look like sand; one pool forum member notes algae coming out of the returns can look a lot like sand.
Do I need to replace the whole filter if sand gets into the pool?
Usually not. Laterals and standpipe assemblies are replaceable parts. A cracked tank is a different story, but that usually shows up as a leak.
Sources
Last reviewed October 12, 2026. Sand amounts and listings change; check your filter’s label or manual before you buy, and follow the maker’s instructions.