Cloudy, Foamy or Green Hot Tub Water? A Troubleshooting Guide for UK Owners

Autumn is a busy time for hot tub water. Evening soaks get longer and more frequent, leaves and garden debris blow in every time the cover comes off, and heavy rain can top up and dilute the water. It's no surprise this is when owners start telling us their water looks cloudy, has a layer of foam or has turned green.

Most water problems have a simple cause and a simple fix. The trick is to diagnose before you dose. Adding chemicals at random usually makes things worse. This guide shows you how to read what your water is telling you and put it right.

Safety first: If your water is green, has a strong smell, or you can't get a sanitiser reading on your test strip, don't use the spa until it's fixed. Always add chemicals to the water, never water to chemicals. Add one product at a time with the jets running, and never mix chemicals together. Follow the instructions on each label.

Before you add anything: two quick checks

1. Test the water

Start with a fresh 3-in-1 Test Strip. It checks your sanitiser, pH and total alkalinity in one go, and the free app turns the reading into clear next steps. Write the results down so you can see whether your changes are working.

Most cloudy, foamy and green water comes down to one of three things:

• Low sanitiser: there isn't enough chlorine or bromine to deal with what's in the water.
• pH or alkalinity out of range: aim for a pH of 7.2–7.6. Outside that range your sanitiser works poorly and the water can turn dull or milky.
• Too much organic load: body oils, lotions, cosmetics, detergent residue and leaves build up faster than the filter and sanitiser can cope with.

2. Check the filter and the age of the water

A dirty filter can't trap fine particles, so they stay in the water and make it look hazy. Take the cartridges out and look at the pleats. If they're grey, greasy or full of debris, that's very likely part of the problem. Our guide to how often to clean your hot tub filter covers the routine.

Also think about when you last drained and refilled. If the water has been in for several months and the spa has had a lot of use, the most effective fix may simply be a fresh fill (see below).

Cloudy or milky water

What causes it

• Low or used-up sanitiser
• High pH or alkalinity, which often makes water look milky rather than just hazy
• A dirty or worn filter
• Fine particles that are too small for the filter to catch
• Organic build-up after heavy use, such as a weekend with family and friends

How to fix it

1. Clean the filters. Rinse them thoroughly with a hose, working between the pleats. For a deep clean, soak them overnight in Canadian Spa Hot Tub Filter Cleaner, then rinse well and let them dry completely. If the pleats are frayed or flattened, replace the cartridge. You'll find yours in our Hot Tub Filters range.
2. Balance the water in the right order. Adjust alkalinity first, then pH, then sanitiser. If alkalinity is low, use Alkalinity Booster. If pH or alkalinity is high, use pH Down. Run the jets for 15–30 minutes after each adjustment, then test again. Our step-by-step chemistry guide explains the order in more detail.
3. Restore your sanitiser. Bring chlorine or bromine back up to the level your test strip and app recommend. If you use chlorine, Chlorine Granules dissolve quickly. Add them with the pump running.
4. Shock the water. Non-Chlorine Spa Shock oxidises the oils and organic waste the filter can't remove, and it helps your sanitiser work properly again without raising your chlorine level. It's the go-to fix after heavy use, and it also deals with musty smells. Read more in our guide to cloudy or musty water.
5. Clarify if any haze is left. Once the water is balanced and sanitised, Spa Clear binds tiny particles together so the filter can catch them. It works best straight after you've cleaned the filters.

Give the spa a full filtration cycle with the cover open slightly, then test again. If the water still hasn't cleared after 24–48 hours, go back to step 1. A filter that's still dirty is the most common reason.

Foamy water

What causes it

Foam is the build-up of things that don't belong in the water, churned up by the jets. Common culprits include:

• Soap and shampoo residue on skin and hair
• Laundry detergent and fabric conditioner left in swimwear
• Body lotions, make-up, hair products and fake tan
• Water that has been in for a long time and is saturated with dissolved solids
• Low sanitiser, which leaves organic matter in the water for longer

How to fix it

1. Knock the foam down. Shake Foam Free (Defoamer) well and squirt it where foam is forming. It sinks the pollutants and carries them to the filter, so you can clear the bubbles without draining.
2. Treat the cause. Defoamer only deals with the symptom. Test and balance the water, clean the filters and shock it as described above to remove the oils and residue that cause the foam.
3. Soak up surface oils. A Spa Ball sits in the filter compartment and absorbs oils and residue from the surface, which helps reduce foam and odours. When it sinks, it's full and needs replacing.
4. Stop it at the source. Ask everyone to shower before they get in. Rinse swimwear in clean water only, with no detergent, before each soak.

If foam comes back within a day or two of treatment, the water is probably saturated. A drain and fresh fill is the answer. If the water smells soapy or perfumed as well, our guide to why your hot tub smells explains what to do.

Green water

What causes it

Green or green-tinged water is almost always caused by algae or bacteria growing because there isn't enough sanitiser in the water. It often happens after a few days without testing, a holiday, or a power interruption that stopped filtration. Green water isn't safe to use.

How to fix it

1. Keep everyone out until the water is clear and testing correctly.
2. Remove the filters and clean them thoroughly, or replace them. A filter that has been sitting in green water will reintroduce contamination.
3. Balance pH and alkalinity first so your sanitiser can work.
4. Raise the sanitiser level substantially, following the shock-dosing instructions on your chlorine or bromine product. Run the jets with the cover open to let gases escape.
5. Filter, test and repeat. Keep the circulation running, then retest. Use Spa Clear to help the filter collect the dead particles.

If the water is a deep green, has a strong smell, or you can see slime on the shell or the filter housing, a drain, flush and refill is usually quicker and more reliable than trying to treat it.

When to drain, flush and refill

Sometimes no amount of dosing will rescue tired water. It's time for a fresh start if:

• the same problem comes back within days of treatment
• the water has been in for several months with regular use
• you're dealing with persistent foam, a stubborn smell or heavy green water

Before you drain, use a pipe cleaner such as Spa Flush, following the instructions on the label. It breaks down the biofilm and fatty deposits inside the plumbing, which would otherwise contaminate your new water straight away. Then drain, wipe down the shell, deep-clean or replace the filters, and refill.

Once the spa is full, balance the water, add sanitiser, and use Control (Stain and Scale Inhibitor) if you're in a hard-water area. Check your owner's manual on our Owners Manuals & Downloads page for your model's drain and refill procedure. After a refill on a cold autumn day, the spa will take a while to come up to temperature. If it doesn't seem to be heating at all, work through our hot tub not heating guide. In a hard-water area, our guide to hot tub limescale explains how much Control to add on a fresh fill.

Prevention: keep your water clear all winter

• Test two or three times a week, and after every heavy-use session.
• Clean your filters regularly and deep-clean them with Filter Cleaner every time you drain and refill.
• Shower before soaking and keep swimwear free of detergent.
• Shock after heavy use to clear organic build-up before it turns into cloudiness or foam.
• Keep the cover on and clear leaves off it before you open it, so debris doesn't end up in the water.
• Keep everything to hand. Our Starter Hot Tub Chemical Kit and Complete Hot Tub & Spa Chemical Kit put the essentials in one box, or browse our full Essential Chemicals range.

Quick diagnosis: symptom, cause, fix

Symptom	Likely cause	Fix
Milky or cloudy	Low sanitiser, high pH or a dirty filter	Test, balance alkalinity then pH, clean the filter, shock
Foam when the jets run	Soaps, lotions or detergent in swimwear; old water	Shower before soaking, rinse swimwear, drain if it persists
Green tint or slime	Algae from low sanitiser	Shock and filter; drain, flush and refill if deep green
Strong chlorine smell	Used-up chlorine, not too much	Shock and leave the cover open for 30 minutes
Itchy skin or stinging eyes	pH out of the 7.2 to 7.6 range	Correct pH
Comes back within days	Biofilm in the pipes or tired water	Spa Flush, then drain and refill

Water problem FAQs

How long does cloudy water take to clear?

Often within a day of balancing, shocking and running the filtration, if the filter is clean. If it is still cloudy after a couple of days, clean or replace the filter and test again.

Can I use the hot tub while the water is cloudy?

Wait until the water is clear and the readings are back in range: pH 7.2 to 7.6, alkalinity 80 to 120 ppm and free chlorine 1.0 to 1.5 ppm.

Is green water dangerous?

It means the sanitiser has failed and algae is growing. Do not use the tub until it has been treated or drained and refilled.

Still having water problems? We're here to help

If you've tested, balanced, cleaned and shocked and the water still won't stay clear, there could be a problem with circulation, ozone or UV equipment, or the filtration cycle settings. Our Hot Tub Health Check gives your spa a full check-over, or visit our Hot Tub Servicing page or contact us. Have your spa model and your latest test strip readings ready.