When to Change Pool Filter Sand (and Should You Use Glass?)

Filter sand is easy to forget about. It sits inside a closed tank and nothing tells you on a particular date that it has worn out. Yet worn sand is one of the most common reasons a pool stays dull no matter how much chlorine goes in. This guide explains how to tell when your sand needs replacing, how to find out what your filter takes, what the job involves, and what to think about if you are considering glass or another alternative media.

What the sand is doing, and why it wears out

In a sand filter, pool water is pushed down through a bed of specially graded silica sand. The sharp edges of fresh grains catch fine dirt, dead algae and other particles, and clean water passes out through slotted collectors called laterals at the bottom of the tank.

Two things wear that bed out. The grains gradually round off, and smooth grains let fine particles slip through. And calcium from hard Highveld water, sunscreen, body oils and dead algae glue the grains into lumps. Water takes the easy route around the lumps, forming channels straight through the bed, and a channelled filter barely filters at all. Backwashing lifts loose dirt out of the sand, but it cannot sharpen a grain or break up a bed that has set hard.

Signs it is time to change the sand

The pool usually tells you before anything else does. Look for these:

  • The water stays dull or slightly cloudy even when chlorine and pH are in range
  • The pressure gauge climbs back up soon after every backwash
  • The clean reading straight after a backwash is higher than it used to be
  • Backwashing makes little difference, or needs doing far more often than before
  • A green pool treatment works, then the water clouds over again soon afterwards
  • Sand collects on the pool floor near the return inlets
  • When the filter lid is opened, the top of the bed is crusted, cracked or pulled away from the tank wall

Cloudy water has other causes too, from high pH to an undersized pump run time, so rule those out first. Our article on cloudy pool water causes and fixes works through them in order. If the chemistry is right, the pump runs long enough and the water is still dull, the sand is the next suspect.

How often: every few years, not on a fixed date

The usual guidance is that filter sand needs replacing every few years. There is no honest single number, because the life of the sand depends on how the pool is used and looked after:

  • Water hardness. Most Gauteng municipal water carries a fair amount of calcium, and calcium is what cements a sand bed.
  • Water balance. Keeping pH and total alkalinity in range slows scaling in the filter as well as on the tiles.
  • Bather load. A pool used every day by a family, or by a complex, loads the filter with far more oils than one used on weekends.
  • Green pool episodes. Filtering out a large algae bloom puts a heavy load of organic material into the bed.
  • Backwashing habits. Backwashing on the pressure gauge, and always rinsing afterwards, keeps the bed cleaner. Our step-by-step guide on how to backwash a sand filter covers the details.

If you do not know when the sand was last changed, it is worth having the filter opened and looked at.

How to find your filter's bag count

Filters are sized by how many bags of filter sand they take, and that number decides how much media goes in and what a sand change costs. To find yours:

  • Look for a label on the side of the filter tank. It usually states the model and the media quantity, though the sun fades these labels.
  • Look up the model number in the filter manual or the manufacturer's documentation.
  • If there is no readable label, take a photo of the whole filter and valve and send it to us on WhatsApp, and we will identify it.

Do not simply fill the tank to the top. The correct level leaves space above the bed so the sand can lift and move during a backwash. An overfilled filter backwashes poorly and can push sand into the valve.

What a sand change involves

A sand change is heavier and fiddlier work than most people expect. In outline:

  • The pump is switched off and isolated, and the multiport valve is removed from the top of the tank.
  • The old sand is dug out, often by hand and often set hard, taking care not to strike the laterals or the standpipe.
  • The laterals and the standpipe are inspected. A cracked or broken lateral is replaced, because it lets sand escape into the pool and ruins new media.
  • The tank is rinsed clean and the standpipe opening is covered so no sand falls into it.
  • The new media is loaded to the correct level for that filter.
  • The valve is refitted with its seals checked, and the filter is backwashed and rinsed to settle the bed and clear the fine dust that comes with new media.
  • With the pump running on filter, the new clean pressure reading is noted.

The laterals: the part people forget

The laterals are the slotted fingers, usually plastic, that sit at the bottom of the tank and let clean water out while keeping the sand in. They become brittle with age and sun exposure, they can crack if the sand has set hard and is dug out carelessly, and they can break if the pump is run against a closed valve. A single broken lateral lets sand pass into the return lines and onto the pool floor.

If you notice sand in the pool, new media alone will not fix it. The laterals need checking while the tank is empty.

Glass media and zeolite: what to know

Sand is not the only media sold for sand filters. Two alternatives come up often.

Glass media is crushed and graded glass, often recycled, made specifically for pool filters. It is sold as an alternative to silica sand and its suppliers describe benefits such as resistance to clumping. Zeolite is a natural porous mineral that is also sold as a filter media, with its own grading and handling instructions.

We are not going to put numbers on how much better either one performs, because that depends on the product, the filter and how the pool is run. What matters more is this:

  • Follow your filter manufacturer's guidance. Some filters specify which media they are designed for, and the quantity of an alternative media is not necessarily the same as the sand bag count.
  • Follow the media supplier's instructions on grading, fill level and backwashing.
  • A different media will not fix broken laterals, a worn valve, poor water balance or a pump running too few hours.

If you would like something other than silica sand, tell us when you ask for a quote, so we can check your filter's manual and confirm what we would load.

Sand change prices by bag count

Our sand change and filter service is priced by the size of your filter, which is the figure on the tank label:

  • 3-bag filter: R1,450
  • 4-bag filter: R1,550
  • 5-bag filter: R1,650
  • 6-bag filter: R1,750

A broken lateral, a worn valve or other parts found during the job are quoted to you before they are replaced.

Doing it yourself versus having it done

Changing filter sand yourself is possible, but go in with your eyes open. Bags of filter sand are heavy, and so is the old sand coming out, usually from an awkward pump room or a tight corner of the garden. Old sand that has set hard has to be broken up in a narrow tank without damaging the laterals, and a lateral broken during the job means another trip for parts. The standpipe must be kept clear of sand, the fill level must be right, and the valve seals must seat properly or the filter leaks. You also need somewhere to dispose of the old sand.

If you are comfortable with all of that, follow the filter manual. If not, we do sand changes across Centurion, Pretoria and Midrand.

If the filter itself needs replacing

Sometimes the problem is the tank: a crack, a split lid, or a filter that is simply too small for the pool. The sand filters in our online shop can be installed at a fixed fitting price. A filter should be matched to the pump, so if one changes we check the other.

Getting help

If your pool will not clear and you suspect the sand, WhatsApp us on 081 577 5051 with a photo of the filter label, the gauge reading after a backwash, and your area. Sand changes start from R1,450 for a 3-bag filter, and we will tell you what we find inside the tank before any extra part is fitted.

More articles