Why Your Hot Tub Is Turning Green (and What to Do About It)

Jennifer Rhodes

By Jennifer Rhodes · Updated

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Ideally, your hot tub should be a place where you can kick back and unwind in clean water. And that means you want yours to be as crystal clear as possible.

The most likely reason your hot tub is turning green is because of an algae build-up. Usually, you can get your water clear again by either adding sanitizer or draining and cleaning your tub. However, a green hot tub can also be due to copper, iron, and other minerals in your spa's water.

To help, this article dives into why your water may turn green—and how to fix it.

Reasons why your hot tub is turning green

The most common culprit behind a green hot tub is algae. And unfortunately, this yucky plant can come from several different sources.

Here are the most common causes of hot tub algae:

  • Dirty filter: If your filter is old or not recently rinsed, it will be much less effective at preventing algae. Built-up debris in your filter may even start to grow the plant.
  • pH imbalance: Algae can thrive in your hot tub if the pH is out of balance—especially if your water lacks total alkalinity which acts as a pH buffer.
  • Plant fertilizer: Have you treated the plants near your tub with fertilizer recently? If so, you may have inadvertently supercharged any algae in the water.
  • Sunlight: Algae uses sunlight to grow and spread effectively. As a result, hot tubs exposed to the sun tend to turn green faster.
  • Lack of maintenance: Regularly sanitizing and draining your tub is crucial for keeping algae away.

Another reason your hot tub may turn green is the presence of minerals, such as copper and iron. This is especially likely if you use a well water system since they often carry more heavy metals.

How to fix green hot tub water

You no doubt want to get rid of that nasty green water. And thankfully, there are plenty of simple ways to do just that.

Here's how to fix a green hot tub:

  • Sanitize your spa: Getting your hot tub back to normal can be as easy as adding a little spa sanitizer. Putting some in weekly is a great way to keep your water crystal clear and clean.
  • Replace your filter: On average, hot tub filters ought to get deep cleaned every 1-3 months, and replaced yearly. Otherwise, debris may start to pile up, making it easier for algae to spread.
  • Drain and scrub your tub: For severe algae problems, it's wise to do a spa purge to clean inside the pipes and then drain your tub completely. Before filling it back up, scrub at any green spots on the shell with a spa surface cleaner.
  • Clean the jet nozzles: Algae and molds often hide and spread from your spa's jet nozzles. So try using a toothbrush to scrub them out periodically. You can also remove the jets and soak them in white vinegar overnight.

If the above doesn't help, that may mean you have an overabundance of minerals in your water. In that case, adding a metal remover to your hot tub should do the trick.

An even better option is a hose attachment that will filter the water while you are filling your tub. This will reduce the mineral content, and help to minimize any future chance of calcium build-up.

Is green hot tub water dangerous?

Most of the time, algae itself is in no way dangerous. As long as you don't eat it, it's usually no more toxic for humans than grass or moss. In fact, many people even tout algae as a healthy ingredient in skin care products!

However, that doesn't mean you should be doing cannonballs into it.

One reason is that when algae can grow in your water, so can other things. For example, harmful bacteria or mold might also take residence in your spa. This problem is especially likely if your water looks murky or smells foul in addition to being green.

As a result, you should avoid getting in at all costs—especially if you have any open cuts or sores. Otherwise, you may expose yourself to infection. And try to keep your pets away to ensure they don't drink any on accident either.

Additionally, some people are severely allergic to this plant. So to be on the safe side, always attempt to eliminate algae as soon as you see it.

How do I keep my hot tub crystal clear?

Getting rid of algae is one thing, but it can always come back. So it's a great idea to take preventative measures to keep this annoying plant away.

Below are ways to stop algae from growing in your spa:

  • Sanitize regularly: Optimally, aim to put sanitizer into your spa (also known as shocking your spa) at least weekly, and after every use. Doing so will help eliminate any organic matter that tries to grow.
  • Rinse your filter: You should remove and wash your spa's filter every couple weeks. That way, built-up debris won't clog it.
  • Refill your tub regularly: Algae is more likely to grow in old, dirty water. So aim to drain and refill your hot tub every 3-4 months.
  • Keep the cover on: Try to keep your hot tub covered whenever you're not using it. Otherwise, contact with sunlight can help algae grow faster.
  • Test weekly: It's easier for algae to grow in water with a chemical or pH imbalance. As a result, you should test your water weekly to detect problems sooner.

What other colors of hot tub water mean

If left untreated, green hot tub water often turns other colors, such as yellow or brown. And if that happens, you might be curious what those different colors mean:

  • Yellow: A yellow hot tub usually also indicates algae growth. Thankfully, this means you can typically get rid of it the same way you do green water.
  • Brown: Spa water can turn brown due to dirtiness or the presence of excess minerals. So ensure that you fill with clean water and rinse your filter often to prevent debris build-up.
  • Orange: Do you use a well water system? If so, the iron in your water may turn your hot tub orange. However, using a metal stain remover for spas should remedy the problem.
  • Pink: Pink slime bacterias often grow on the surface of hot tub shells. Since they're hardy, getting rid of them requires a potent chlorine shock, thorough deep clean, and filter replacement.

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