Cartridge or Sand Filter for a Hot Tub? Which Is Right for Your Build

Last updated: September 2026

Cartridge or sand? It’s one of the first questions people ask me once they’ve worked out the plumbing for their DIY hot tub. Both work. Both keep water clear. But they suit very different jobs, and picking the wrong one means more work, more wasted water or a filter that simply isn’t up to it.

In this guide I’ll explain how each type works (plus DE, which often gets muddled up with cartridges), compare them side by side, and tell you which I’d fit to a DIY hot tub, a spool or a plunge pool.

I’ve also covered this on video, so if you’d rather watch than read, here it is:

What is a cartridge filter?

A cartridge filter is a cylinder of pleated polyester fabric with plastic end caps and a hollow core. Water is pushed (or pulled) through the pleats from the outside in, the fabric catches the dirt, and the clean water leaves through the core and heads back to the tub.

In a shop-bought hot tub the cartridge usually sits in the skimmer, behind a weir door. On most DIY builds it lives in a separate filter housing in the control room, often with a pressure gauge on the lid. That’s how I’d do it, because it’s easier to service and you can size the filter properly for the tub.

The pleats give a lot of surface area in a small space, which is why cartridges are rated in square feet. For most DIY-built hot tubs, a 50 sq ft cartridge is more than enough to keep the water clean.

How long does a cartridge last?

For a hot tub, expect to replace the cartridge every 12–24 months. How long yours lasts depends on:

• How much the tub is used. More bathers means more oils, skin and hair in the pleats.
• Your water. Hard water scales the fabric up faster.
• Your chemistry. Stable pH and sanitiser levels mean less gunk for the filter to deal with.
• How you clean it. A garden hose is fine. A pressure washer tears the fabric and drives dirt deeper into it, which Trouble Free Pool also warns against.

Keeping a spare and swapping them over is the easiest way to make both last longer. The full routine (weekly rinse, monthly clean, overnight soak at each water change) is in my guide on how to clean a hot tub filter cartridge.

What is a DE filter?

DE filters often get lumped in with cartridges, but they’re a different thing. DE stands for diatomaceous earth, a fine powder made from the fossilised skeletons of tiny algae called diatoms. Inside a DE filter are fabric-covered “grids” or “fingers”. You add DE powder through the skimmer, it coats the grids, and that coating does the filtering. Under a microscope, each grain is full of tiny pores, which is why it catches such fine particles.

DE gives the finest filtration of the three, but it’s a pool filter. When you backwash it you lose the powder and have to add more, and you need to handle the dry powder carefully (wear a dust mask). I don’t know anyone who has fitted DE to a DIY hot tub, and I wouldn’t.

What is a sand filter?

A sand filter is a tank filled with filter sand. Water from the pump enters at the top, runs down through the sand bed, gets collected by slotted “laterals” at the bottom, and goes back to the pool. The dirt stays trapped in the sand. A multiport valve on the top or side lets you switch between filter, backwash, rinse and other settings.

You don’t clean a sand filter by taking it apart. You backwash it: the valve reverses the flow so water goes up through the sand, lifts the dirt out and sends it to waste. Then a short rinse resettles the bed before you go back to filter. Hayward’s manual says to backwash when the pressure gauge reads 8–10 psi (0.55–0.69 bar) above the clean reading, for around two minutes, followed by 30 seconds to a minute on rinse. Always switch the pump off before you move the valve.

How often do you change the sand?

Not every year. Filter sand typically lasts 3–5 years, sometimes longer on a lightly used pool. Change it when the pressure climbs back up quickly after a backwash, the water won’t clear, or the sand has clumped into lumps. Use the grade the filter maker specifies, which is usually No. 20 silica sand (0.45–0.55mm). There’s much more on backwashing, rinsing and glass media in my sand filter guide.

Cartridge vs sand vs DE: side by side

	Cartridge	Sand	DE
Typical filtration	10–20 microns	20–40 microns	1–3 microns
How you clean it	Remove, hose off, soak in cleaner	Backwash and rinse	Backwash, then add fresh DE
Water used cleaning	A bucket or a hose	Backwash goes to waste	Backwash goes to waste
Media replacement	Cartridge every 1–2 years (hot tub)	Sand every 3–5 years	Powder after every backwash
Best for	Hot tubs, small pools	Spools, plunge and swimming pools	Pools where clarity is everything
Hot tub friendly?	Yes, the standard choice	Possible, with its own pump	Not really

Micron figures and sand life are typical values from In The Swim’s filter comparison. Individual products vary.

Which filter should you use on a DIY hot tub?

For a DIY hot tub, I recommend a cartridge filter, and it’s what almost all my customers fit. Here’s why:

• It filters finer. Hot tubs have a lot of people in a small volume of warm water, so body oils and fine particles build up fast. The finer the filter, the better.
• No backwashing. A backwash dumps water to waste. In a pool that’s a small percentage. In a hot tub holding 2,000–3,000 litres (530–790 US gallons), a couple of minutes of backwash is a noticeable chunk of water, and it’s water you’ve paid to heat and treat.
• It suits the pumps. A cartridge housing works happily on a circulation pump or the low speed of a two-speed pump. A sand filter needs decent flow to work and to backwash properly.
• It’s simple and cheap. A housing and a couple of cartridges cost less than a sand filter with a multiport valve, and servicing takes ten minutes with a hose.

Can you use a sand filter on a hot tub?

Yes, but it needs its own dedicated pump, which fits naturally on a build with a separate filtration pump and jet pump. You also need somewhere for the backwash water to go, and you’ll be topping up and reheating after every backwash. I’ve gone into this in more detail in Can I use a sand filter on my DIY hot tub?, and there’s more on pump layouts in How many pumps do you need?

When a sand filter is the better choice

Once you get into bigger volumes, the balance flips. For a spool, cocktail pool, plunge pool or full swimming pool, a sand filter makes a lot of sense:

• It handles large volumes and a heavy debris load (leaves, grass, garden dust) without clogging quickly.
• There’s nothing to replace for years. You backwash when the gauge tells you to.
• Backwash water is a small fraction of a pool’s volume.

If you want finer filtration from a sand filter, you can swap the sand for a glass media, or add a small amount of pool-grade DE to the sand bed. Both are covered in the sand filter guide. And if you’re building a combined hot tub and pool, keep the two plumbing systems separate, each with its own filter. I’ve explained why in Why pool and hot tub plumbing should remain separate.

Other things to weigh up

• Your time. A sand filter needs a backwash every so often, which only takes a few minutes. A cartridge needs taking out and hosing off, and a soak now and again. Neither is a big job.
• Your budget. Sand is usually the cheaper filter to run over time on a pool, because there’s no cartridge to buy. On a hot tub, cartridges are cheap and a sand filter setup costs more to buy.
• Water restrictions. If you’re somewhere with hosepipe bans or water limits, a cartridge’s low water use matters.
• Pressure gauges. Whichever you fit, put a pressure gauge on it and note the reading when it’s clean. It tells you when it needs cleaning far better than a calendar does.

Common filter mistakes

• Undersizing the filter. Size it for the flow of the pump that runs through it, not just the water volume.
• Pressure washing cartridges. It shreds the pleats. Use a garden hose at an angle.
• Moving a multiport valve with the pump running. It damages the valve’s gasket. Pump off first, every time.
• Backwashing too often. A slightly dirty sand bed actually filters better. Wait until the pressure has risen.
• Expecting the filter to fix the chemistry. Filters remove particles, not bacteria. Your sanitiser does that. See my hot tub chemical levels guide.

Troubleshooting

Problem	Likely cause and fix
Cloudy water	Dirty or worn cartridge, sand due a backwash, or chemistry out of range. Clean the filter, then test and balance. More in cloudy water in a hot tub.
FLO or flow errors on the spa pack	A clogged cartridge restricting flow. Clean it first. See hot tub FLO error.
Pressure climbs back within days	A worn-out cartridge, or clumped sand. Replace it.
Sand in the pool or tub	A cracked lateral in the sand filter, or the wrong grade of sand. Check the laterals when you change the sand.
Very low pressure	A blockage before the filter (a full skimmer basket, a closed valve) or an air leak on the suction side.

Planning your own build?

The filter is one small part of getting the plumbing right. My DIY hot tub plans include the full plumbing layout with the filter, pumps and heater sized for the tub, plus a parts list and the video course. There’s also a good overview in How does hot tub plumbing work?

Need a replacement cartridge, housing or filter sand? You’ll find them at parts4tubs.co.uk in the UK and parts4tubs.com in the USA.

FAQs

Is a sand filter or cartridge filter better for a hot tub?

A cartridge filter. It filters finer, doesn’t need backwashing, and suits the small, warm, heavily used volume of water in a hot tub.

Do sand filters filter better than cartridges?

No. A typical sand filter catches particles down to about 20–40 microns, and a cartridge about 10–20. Sand wins on handling large volumes and heavy debris, not on fineness.

How often should I change hot tub filter cartridges?

Usually every 12–24 months, sooner if the pleats are flattened or torn, or the pressure rises again within days of cleaning.

How often should I change the sand in a sand filter?

Typically every 3–5 years, not annually. Change it when backwashing no longer brings the pressure down or the water won’t clear.

Is a DE filter the same as a cartridge filter?

No. A DE filter uses a coating of diatomaceous earth powder on fabric grids and is backwashed like a sand filter. A cartridge is a pleated fabric element you take out and rinse.

Still not sure which filter suits your build? Drop your question in the comments below. I read them all.

Cheers,
Andi

You can also find me on my socials;

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi