Filter sand does not last forever: over the years the bed can clog or cake and the filter has to be backwashed more and more often to keep its pressure normal. This page explains when it is time to replace the sand, which sand to use, and how to do the swap step by step, based on Hayward's support answers and the Hayward and Pentair filter manuals.
The short version: Hayward says you generally need to replace the sand every 3 to 5 years: longer if the water stays clear, sooner if you keep having to backwash to hold normal pressure. Use only No. 20 silica pool filter sand (0.45 to 0.55 mm) in the amount on your filter's nameplate. Switch the pump off and relieve the pressure first, protect the standpipe, fill the tank half with water before you pour, and backwash once before you start filtering again.
When to replace the sand
Hayward Support, answering an owner of its S244S sand filter: "generally you need to replace the sand in your filter every 3-5 years". That is a range, not a date on the calendar. Hayward gives the two signals that move it:
- Longer if you do not see a loss of clarity in the pool.
- Shorter if you are continually having to backwash to keep the pressure in the normal range.
Hayward's S270T filter manual adds a check for one specific problem: if the filter cycles get short (after checking for algae and the chlorine and pH levels), look at the surface of the sand for crusting or caking and remove 1 inch of sand if necessary. If the whole bed is caked or the short cycles keep coming back, that is the moment for fresh sand (our advice).
Before you blame the sand, rule out the simpler causes: Hayward's S270T problem list also points to the skimmer and pump baskets, algae and the chlorine and pH levels. See what high pool filter pressure means.
Which sand to use
| What | What the manufacturers say |
|---|---|
| Type | No. 20 silica filter sand. Hayward: "we only recommend #20 silica pool filter sand in our sand filters". Pentair: "you must use only No. 20 standard silica sand" |
| Grain size | 0.45 to 0.55 mm (both makers); 0.018 to 0.022 inches (Pentair). Hayward: also known as No. 20 or No. ½ silica sand |
| Uniformity | Uniformity coefficient of 1.75 or less (Pentair) |
| Amount | The precise amount on your filter's nameplate (Pentair). Example: Hayward lists 350 lb for its S270T |
How much your filter takes depends on the model; see how much sand a pool filter needs. Sand comes in heavy bags, and Pentair notes that a filter filled with sand and water can weigh several hundred pounds.
As an Amazon Associate we earn from qualifying purchases: see #20 silica pool filter sand on Amazon (check the grade and the bag weight against your nameplate).
Before you start
A sand filter is a pressure vessel. Pentair's manual: never service it while under pressure; always relieve the tank pressure and open the air bleeder before you start. Switch the pump off, and off at the breaker as well (our advice).
Do it yourself or not? Hayward Support, asked how to change the sand in one of its filters, answered: "unless you are familiar with replacing the sand in this product we recommend you allow a professional to do the repair." The steps below follow the manuals; if you are unsure, a pool service can do it.
Have ready: the right amount of No. 20 silica sand, a sand shield or guide for the standpipe (some filters come with one; otherwise a cap or a cup over the pipe works, our advice), a garden hose, a scoop or a wet vacuum, and the filter's manual for your model.
How to replace pool filter sand, step by step
- Switch the pump off and relieve the pressure. Open the air bleeder so the tank is not under pressure (Pentair).
- Drain the tank. Remove the drain cap or spigot at the bottom and let the water run out.
- Remove the valve. On a top-mount filter, loosen the flange clamp and lift off the control valve (Hayward). Keep the valve O-ring.
- Take out the old sand. Pentair's manual says sand may be removed by taking out the entire drain spigot at the bottom and flushing with a garden hose. Many owners scoop it out from the top or use a wet vacuum (our description). Keep the standpipe straight and do not pull on it (our advice).
- Check the laterals. Look at the laterals (the "fingers") at the bottom for breaks or loose parts, and replace any broken ones before refilling (Pentair).
- Cover the standpipe. Cap the internal pipe with the sand shield so no sand falls into it; make sure the pipe sits firmly in the bottom hub (Hayward).
- Fill the tank about half with water. Both manuals say to do this; Hayward explains that the water cushions the falling sand and protects the laterals. Put the drain cap or spigot back in first.
- Pour in the new sand slowly, so its weight does not damage the laterals (Pentair), until you reach the amount on the nameplate.
- Clean the top. Remove the sand guide and wash away all sand around the opening; check that the valve O-ring is in place (Pentair).
- Refit the valve and clamp, with the ports in the right places: pump, waste and return (Pentair).
- Backwash, then rinse, then filter. Hayward's S270T manual: once the water flows steadily out of the waste line, run the pump for at least 2 minutes; this initial backwash is recommended to remove impurities and fine sand particles. Then rinse and return to filter as usual. Open the air bleeder and stand clear of the filter when you restart it (Pentair).
- Write down the new clean pressure. That is your new starting point for the next backwash.
After the swap: do not backwash too often
Pentair's manual says not to backwash solely on a timed basis, such as every three days, and that backwashing too frequently actually causes poor filtration. Pentair names three ways to judge it: a 30% drop in flow on a flow meter (the most accurate), visibly weaker flow at the pool returns, or a pressure rise of 10 psi over the clean reading (the most commonly used, but least accurate). Hayward's S270T manual uses 8 to 10 psi.
Common mistakes
- Opening the filter under pressure. Always relieve the pressure first.
- Using the wrong sand, such as play sand or a different grade. Hayward and Pentair both say No. 20 silica.
- Pouring sand into a dry tank. Fill it about half with water first to protect the laterals.
- Forgetting to cover the standpipe, so sand ends up in the pipe and back in the pool.
- Skipping the first backwash, so fine particles from the new sand go to the pool.
- Guessing the amount instead of reading the nameplate.
Sources
Replacement interval, sand type and the advice to use a professional: Hayward ProSeries sand filter product page (Hayward Support answers, June 2026). Sand grade and amount, loading, the crusting check and the first backwash: Hayward Pro Series sand filter owner's manual (IS270T, Rev. B). Sand specification, laterals, loading, removing sand, pressure warnings and backwash indicators: Pentair Sand Dollar and Cristal-Flo II sand filter installation and user's guide. Points marked as ours are our own advice or description; your filter's manual comes first.
Frequently asked questions
How often should pool filter sand be replaced?
Hayward says generally every 3 to 5 years: longer if the water stays clear, sooner if you keep having to backwash to hold normal pressure.
What sand do I use in a pool filter?
No. 20 silica pool filter sand, 0.45 to 0.55 mm. Hayward only recommends #20 silica in its sand filters, and Pentair's manual says to use only No. 20 standard silica sand.
How much sand does my filter need?
The exact amount is on your filter's nameplate; it depends on the model. See how much sand a pool filter needs.
Why fill the tank with water before adding sand?
Both Hayward and Pentair say to fill the tank about half with water first. Hayward explains that the water cushions the falling sand and protects the laterals at the bottom.
Do I backwash after replacing the sand?
Yes. Hayward's S270T manual recommends an initial backwash of at least 2 minutes once the water flows steadily to waste, to remove impurities and fine sand particles; then rinse before you return to filter.
