How to Clean Your Hot Tub with Baking Soda (Step-by-Step)

Last updated: September 2026

Ever lifted the lid of your hot tub only to find it isn’t ready for a relaxing soak? Cloudy water, a nasty smell or a slimy ring around the waterline can put a stop to your plans. Regular maintenance prevents most of it, but sooner or later every tub needs a proper clean.

Baking soda sounds too simple to work, but it’s a cheap, gentle, shell-safe way to shift stubborn marks. In this guide I’ll show you where baking soda helps, and give you the full drain-and-clean routine around it.

How to tell it’s time to clean your hot tub

Chemistry alone can’t keep a tub clean forever. Even with perfect balance, dissolved solids build up until the water needs replacing. A simple formula (the same one I use in my beginner’s guide to hot tub maintenance) tells you when:

(gallons in the tub, divided by the number of regular bathers) divided by 3 = days between water changes.

For example, a 400 gallon tub used by two people: 400 divided by 2 is 200, divided by 3 is about 66. So drain and refill roughly every two months. As a general rule, every three to four months is a sensible rhythm for a home tub, and sooner if it gets heavy use. Look out for these signs that you should do it earlier:

• Cloudy or muddy water that won’t clear
• A brown or slimy ring of biofilm at the waterline
• A strong “chlorine” smell, which is usually chloramines (chlorine combined with sweat, oils and urine)
• Skin or eye irritation
• Foam that keeps coming back (see foam in a hot tub)

What is biofilm?

Biofilm is a slimy layer of bacteria that sticks to surfaces, mostly inside the plumbing where water doesn’t move much. It builds up from bacteria, body oils and skin cells, and it protects the bacteria from sanitiser, so chlorine or bromine alone can’t shift it. That’s why a line flush before draining matters. It’s also why you should be wary of a secondhand tub: always check the pipework.

Uncontrolled biofilm can harbour nasty bugs, including Legionella and Pseudomonas, so don’t skip the flush if the tub has had a rough time.

What are chloramines?

Chloramines form when chlorine meets ammonia-containing waste such as sweat, body oil and urine. They give off that strong “swimming pool” smell people wrongly think of as clean. It’s actually a sign the water is short of active chlorine. Test for free and combined chlorine, and shock the water to break chloramines down (read hot tub shock). If it keeps happening, the water is probably tired and needs changing.

Steps to clean your hot tub with baking soda

1. Flush the lines

If there’s biofilm in the plumbing, flush the lines first. Add a spa line flush or plumbing cleaner (follow its instructions) to the water and run the jets for about 30 minutes so it circulates through all the pipework. A flush is also worth doing if your jets seem weaker than normal. Then drain as below. If you want the detailed drain process, see how to drain and clean a hot tub.

2. Power down

Switch off at the breaker or isolator. If the pump runs with no water in it, you’ll damage the pump and heater. Don’t switch it back on until the tub is refilled.

3. Drain the tub

Use a submersible pump (under an hour for most tubs) or a hose on the drain valve (several hours). Check your local rules on where the water can go. Chlorinated or brominated water shouldn’t go into storm drains or watercourses. Let the sanitiser fall to almost nothing first, or use a neutraliser. Once it has, the water is fine for watering the garden, but don’t send it towards plants you care about while it still smells of chemicals.

4. Clean the shell

Use a soft, non-scratch cloth or sponge. A gentle spray of a spa-safe cleaner, or a diluted white vinegar solution, loosens most of the scum. Never mix bleach and vinegar, because that gives off toxic chlorine gas. Avoid household cleaners with detergents, oils or fragrances. They leave residues that cause foam. Check your tub maker’s guidance if your shell is acrylic, and don’t use abrasive pads on it.

5. Tackle the problem areas with baking soda

This is where baking soda earns its place. Mix it with a little water into a thick paste, spread it over the stubborn scum line or stained patch, and leave it for 10 to 15 minutes. Rub gently with a damp cloth or soft sponge, then rinse thoroughly. Repeat if necessary. Baking soda is safe for the shell and avoids harsh chemicals. It’s mildly abrasive, so use a light touch on gloss acrylic.

Baking soda (sodium bicarbonate) also raises total alkalinity, which is why it’s a popular alkalinity increaser. That’s another reason to rinse the shell well, so you don’t add an unknown amount to the fresh water.

6. Clean or replace the filters

Filters collect oils, algae and organic matter. Take them out and rinse them with a garden hose, then soak them in a proper filter cleaner and rinse again. Don’t use a pressure washer (it damages the pleats), the dishwasher or laundry detergent. If you have limescale on the filter, soak it in a dilute acid filter cleaner, then rinse well. Swap in a spare filter while the first dries. Filters that no longer come clean should be replaced. Read how to clean a hot tub filter cartridge for the full method. I’d change them about once a year.

7. Refit the filters

Empty and wipe out the filter housing before you put the cartridge back. It’s the spot most people forget.

8. Refill the tub

Fill through the filter compartment, or the skimmer, so the water pushes air out of the plumbing rather than trapping it. That’s how you avoid an air lock (see air lock in a hot tub and how to fill a hot tub the correct way).

9. Power back up

Switch the tub back on once it’s at its normal level. Listen to the pump for the first 15 minutes or so. If anything sounds wrong, you’ll notice straight away.

10. Treat the water

Test the fill water, then adjust in this order:

Step	Target
1. Total alkalinity	80 to 120 ppm
2. pH	7.2 to 7.6
3. Calcium hardness	150 to 250 ppm (see my chemical balancing guide)
4. Sanitiser	Free chlorine 3 to 5 ppm, or bromine 4 to 6 ppm
5. Shock, if needed	See hot tub shock
Cyanuric acid (CYA)	As low as possible. Fresh water resets it to zero

If you have a salt chlorinator, check the salt level after refilling, because tap water already carries a little. Then follow the maker’s guidance. Give the tub a full circulation cycle before anyone gets in, and always follow the label when using chemicals.

11. Keep it clean day to day

• Test the water two or three times a week, and clean the filter every month or two.
• Shower before you get in. It removes oils and lotions that cause foam and chloramines.
• Keep drinks out of the water, especially anything sugary or alcoholic.
• Skim off leaves and debris straight away.
• Keep the cover on, and clean it regularly. See hot tub cover maintenance.

If you’re closing the tub for winter rather than refilling it, read winterizing your hot tub. If the water is cloudy after all this, see cloudy water in a hot tub.

Need parts or filters?

For filters, spa packs and other spare parts, take a look at parts4tubs.co.uk in the UK or parts4tubs.com in the USA. Thinking of building your own tub? My hot tub plans are there when you’re ready.

FAQs

Can you clean a hot tub with baking soda?

Yes, for the shell. A paste of baking soda and water loosens scum and light stains on a drained tub. It doesn’t sanitise or remove biofilm, so it’s part of a clean, not a replacement for one.

Can I put baking soda in my hot tub water?

Only as an alkalinity increaser, when your test shows total alkalinity is below 80 ppm. Add it in small amounts, test again and don’t use it as a cleaner in the water.

How often should I drain and clean my hot tub?

Every three to four months for a typical home tub. Use the formula (gallons divided by bathers, divided by 3) to see how many days between changes for your tub.

What should I not use to clean a hot tub?

Avoid household cleaners with detergents, oils or fragrance, abrasive pads, a pressure washer on filters and anything you can’t rinse away completely. Never mix bleach and vinegar.

Do I need to use a line flush before draining?

It’s a good idea if you’ve never done it, the water is cloudy or the tub has been neglected. It loosens biofilm from the pipework so it drains away with the old water.

Got a question about your own tub? Drop it in the comments below. I read them all.

Cheers,
Andi

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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