Hot tub water yellow
Hot tub water yellow usually points to pollen, yellow algae, or iron in your fill water. Check when the yellow showed up and where it sits: every cause needs its own fix, though only algae requires a very strong shock.
- Mostly in spring, yellow dust appears floating on the surface.
- Pollen
- Normal chlorine cannot kill it, and it sticks to the shell
- Yellow algae
- On well water, the water turns yellow right after a shock.
- Iron
- Dichlor shock rate (28 g for 1,890 L)
- 1 oz per 500 US gal
Signs, likely causes and fixes for yellow water.
Before adding anything, check how the water looks. Floating yellow differs from yellow stuck to the shell, and both differ from clear water with a tint.
| What you see | Likely cause | Fix |
|---|---|---|
| In spring, yellow dust drifts with the wind on the surface. | Pollen | Skim it off, then rinse the filter, shock the water, and keep the cover on. |
| In cracks and corners, a gritty yellow film sticks to the shell. | Yellow (mustard) algae | Drain and scrub after balancing and applying a very strong chlorine shock. |
| On well water, clear water turns yellow right after a shock. | Iron | Metal remover (sequestrant) |
| A yellow-red shade when the bromine pad reads very high | Too much bromine, often with a low pH | Stay out until it drops; raise the pH |
| A yellow ring forms at the water line, or you see yellowish foam. | Body oils, lotion and low sanitizer | Wipe the ring, shock, clean the filter |
The first four rows match Leslie's water color guide. Pollen and algae clues are from Leslie's pollen guide, made for pools, and the foam details are on their foamy, cloudy spa water page.
Surface yellow dust indicates pollen
Of the causes, pollen is the mild one. In spring, spa water gets a tint from it, especially if the cover stayed off long, notes Leslie's. When the wind blows, it moves, collects at the edges, and floats on top. Algae stays fixed to the walls instead of moving.
After skimming with a fine mesh net, rinse the filter which catches the rest. Also, shock the water. Leslie's notes that breaking down pollen can feed algae; find your tub dose in the shock calculator.
Clean the cover too since pollen settles on top of it. To remove tree sap, dirt and pollen, Leslie's beginner's guide suggests a spa cover cleaner. Before folding the cover back, wipe it so nothing slides into the water.
Clearing yellow algae: the steps to take
The stubborn kind is yellow algae, also called mustard algae. It survives normal chlorine or bromine levels and lives in dark, warm water per Leslie's. Across the shell, it spreads in sheets after hiding in small cracks. According to Leslie's mustard algae guide, it feels gritty and looks enough like sand or pollen to cause confusion.
- Start by balancing your water. Parts per million (ppm) is the unit on your test strip; adjust alkalinity to 80 to 120 ppm, then set pH to 7.4 to 7.6. Find the amount for your tub in the chemical calculator.
- Switch off the heater. Leslie's recommends doing this before you shock for algae.
- Apply a large dose of chlorine to shock the water. A very high level is what Leslie's asks for. For a 350 gallon (1,320 litre) tub, use 0.7 oz (20 g), since the EPA-registered dichlor label sets normal shock at 1 oz per 500 US gallons. For a stronger dose, follow the label on your own product.
- Keep the cover off and run the water for several hours. You must let the gas from shocking escape.
- Test the water again on the following day. Shock again if free chlorine or bromine has fallen to 0 ppm by then. Keep repeating this until the level stays steady.
- Drain the tub and scrub it down. Then drain the tub, scrub the shell, wash the cover with bleach, and fit a new filter, says Leslie's. Check how to drain a hot tub for instructions.
Only soak again when free chlorine hits 3 to 5 ppm. Turn on the jets as you add each chemical separately, and never mix two products together.
Well water containing iron
Clear water can get a yellow tint from iron in your fill water. This issue appears most when the tub goes yellow immediately following a shock, according to Leslie's. Higher iron levels turn water brown; the green or brown water page covers that.
Shocking will not solve this problem. Use a metal remover like Spa Metal Free at the dose listed for your gallons. Add it each time you fill, before other chemicals, then run circulation for 4 to 6 hours, per the chemical guide from Leslie's.
Although a hose pre-filter helps with rust and dirt, dissolved iron or copper will remain, according to the Hot Spring owner's manual.
Bromine levels that are very high
Bromine acts as a sanitizer, which is the common chemical used to kill germs. Leslie's explains that extremely high levels can turn water a yellow-red color, especially when pH is low.
Stay out of the tub with the cover open until the bromine pad reads within your normal range. Next, use the pH up guide to raise pH to 7.4 to 7.6. Find the levels to maintain in Bromine vs chlorine.
A ring at the water line or foaming that looks yellow
Seeing a little white foam while the jets run high is normal. Thick, off-color foam that stays once the jets are off means the filter or sanitizer can't keep up, or something got into the water, says Leslie's.
Body oils and dirt usually cause a yellow ring at the water line. Use a clean rag to wipe it off, says the Hot Spring manual. After shocking the water and cleaning the filter, go to hot tub foam if foam continues to appear. If a ring reappears shortly after you clean it, biofilm in the pipes may be the cause.
Ways to prevent yellow water
- Between soaks, leave the cover on, and give the top a cleaning each spring.
- Rinse your filter weekly, or more often when pollen is high.
- Keep free chlorine between 3 and 5 ppm, testing with test strips before every soak.
- Apply a shock treatment about once weekly and following busy soaks.
- Add a metal remover every time you fill from a well.
Common questions
Why does my hot tub turn yellow after shocking?
Well water iron becomes visible mostly after a shock treatment. A metal remover, Spa Metal Free for example, holds it in the water so it no longer colors it.
Why is my hot tub water yellow?
Spring pollen, yellow algae on the shell, or well water iron cause this most often. Body oils and very high bromine levels can also cause the tint. This page has a table at the top that helps you tell them apart.
Is soaking in a hot tub with yellow water safe?
Hold off until you find out what caused it. Very high bromine irritates skin, and algae shows the sanitizer has failed. Test first, and only soak once levels return to normal.
Does shock treatment fix yellow hot tub water?
It resolves pollen and algae issues when you also have balanced water and a clean filter. Iron needs a metal remover and very high bromine needs time to drop, so it fixes neither.