Green Hot Tub Water? Find the Source and a Solution

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Why Spa Water Has a Green Tint

If your hot tub suffering from green spa water, you’re definitely not alone. Every year we have thousands of people looking for solutions to their green hot tub water.

Green Hot Tub Water WordPress

Your spa water can be discolored due to several factors, but usually a chemical imbalance is at fault. Algae can be a cause of green hot tub water, but that is normally not the reason.

Let’s look at the other sources and offer a solution for you to fix your green spa water.


Some common reasons you’ll find green water in a hot tub are:

  • Algae
  • Excessive metal content
  • Low sanitizer levels
  • Low pH


Most people assume their spa’s green water is caused by algae, but it is a very rare occurrence in hot tubs due to the use of covers.

Algae is an aquatic plant that needs sunlight to thrive, making it more common in pools or in-ground gunite spas.


Algae can spread quickly if the cover is removed or left off during the day, the filter cartridge is dirty or if the sanitizer levels are consistently low.

But how can you tell if the cause of green water is algae or not?

Algae growth in a hot tub is accompanied by a slimy coating on the inside of the spa.

Algae comes in many different colors also, such as black or mustard. If you notice a slippery feeling inside the spa, it’s probably algae. It can be transferred via bathing suits, so be sure to wash your swimwear if you were recently in a lake, river or the ocean.

How to Remove Algae from a Hot Tub


  1. If the algae doesn’t seem too bad, you can dose spa water with an initial treatment of Spa Algaecide which may eliminate visible algae growth.
  2. For preventative measures, add 1 – 2 fluid ounces for every 500 gallons of spa water once a week. Follow directions on bottle for clear instructions of use.


  1. PLUMBING – Perform a Spa System Flush. The algae could be hiding in the plumbing. If flush product is not used, algae can continue to spread even after refill and cleaning.
  2. SHELL – After using the system flush, drain and clean inside of spa with EcoTub CleanAll or other non-foaming cleanser. Do not use bleach, vinegar or household cleaners. These products can damage the spa shell and will alter water chemistry.
  3. FILTER – Perform a thorough deep clean on your filter (see how here) or replace the filter cartridge, especially if it is more than 1 year old. Replace with Antimicrobial filters, which have advanced filter media to inhibit the growth of bacteria.
  4. REFILL – After flushing the plumbing and cleaning the spa shell and filter, refill the hot tub.
  5. BALANCE – Test the water’s Total Alkalinity and pH, adjust to normal levels.
  6. PREVENT – Use Spa Algaecide for weekly preventative measures as directed on bottle.


The most common cause of green spa water is excessive metal content. Water from wells or the municipal system can contain high levels of metals such as copper or iron.

Hot tub water turns green after you shock the hot tub because the oxidization reacts with copper turning it the green tint.

Copper plumbing

How can you tell if it’s excessive metal content? If your TA and pH are in balance, the spa water will be clear with a green tint, like food coloring was added to the water.

When the weather warms up, your plumbing and garden hose can start to carry these metals from the water lines. Temperature can also affect the water table, causing metals to become more evident.

How to Remove Excessive Metal Content


If you recently refilled your hot tub and the water has a light green tint, simply remove it with these steps:

  1. Test Total Alkalinity, pH and Calcium Hardness and adjust to normal levels.
  2. Add CuLator SpaPak to filter/skimmer area. This will be the preventative step to removing clear green water in your hot tub.
  3. Retest water chemistry levels including sanitizer and adjust where necessary.


Since it is unlikely the water source is going to change, follow these steps at your next refill:

  1. REFILL – use a hose end filter such as PreFresh to reduce metal impurities.
  2. REMOVE – Add Metal Free as directed on bottle to remove the spa of stain-causing metals such as copper, that the PreFresh did not catch (Do not treat with Metal Free if using Cleanwater Blue system, treat with Cleanwater Purge instead).
  3. PREVENT – Add Chitosan Natural Clarifier weekly, as preventative maintenance.
  4. SHOCK – Use Oxy-Spa non-chlorine shock after each use to maintain healthy spa water.
  5. Add CuLator SpaPak to filter/skimmer area.


While maintaining the proper level of sanitizer at all times is essential, life happens and spa maintenance can get left by the wayside for months.

Whether you use bromine, chlorine or another sanitizer, the green water could be caused by low sanitizer levels or by not shocking frequently enough.

Shocking allows your sanitizer to perform at peak efficiency and in best practices should be added once a week or after each spa use. You can shock your spa with  dichlor granules or a non-chlorine shock such as Oxy-Spa.

Raise Low Sanitizer Levels

  1. Test water for sanitizer level.
  2. Depending on sanitizer used, adjust to meet recommended amount.
  3. Allow water to circulate for 24 hours then retest and adjust as necessary.
  4. Test weekly to maintain proper hot tub water chemistry.

Just keep in mind that shocking your spa will gradually lower the pH level but, it is necessary to destroy any dead organic matter killed by the sanitizer.


Sometimes low pH can induce a green tint to your spa water. With an imbalance of pH, it can allow bacteria to build and discolor the water. If the pH is too low, the water is acidic and over time it can erode plastic and metal equipment.

Related to excessive metal content, low pH levels can cause copper to dissolve from your heating element into your spa water.

How can you tell if it’s low pH? By using test strips to monitor your pH level.

Adjust Low pH

  1. Test water for Total Alkalinity and pH level.
  2. Begin by adjusting Total Alkalinity. If TA is low or high, adjust first, which will help regulate pH. Remember, after adding the appropriate chemical, run spa on high speed with blower on (if applicable) to aerate water.
  3. Retest spa water and adjust where necessary.
  4. Maintain proper spa water chemistry by testing weekly.
  5. When pH is in balance, follow directions for Excessive Metal Content to remove the green cloudy hot tub water.

Total Alkalinity has a direct and huge impact on pH. When TA is low, pH bounce can be impossible to control. When TA is high, pH drifts upward and makes it difficult to lower. Learn more about TA and pH.


You’ll want to follow these guidelines and test weekly for proper chemistry levels in your spa. By keeping your hot tub water and sanitizer regulated, you’ll reduce the risk of creating discolored water.

Spa Water Chemistry

Routine draining every 3 – 4 months is recommended (or more frequently depending on usage, bather load, etc.) to keep water as healthy as possible.

To Recap…

  • Green tinted spa water isn’t always algae.
    • Algae is an aquatic plant that is slimy and attaches to the sides of the spa.
    • Algae is less common in hot tubs due to the use of covers.
  • Clear green spa water can be related to high levels of copper from the water source.
  • Hot tubs with cloudy green water can be caused low sanitizer levels.
  • Why is hot tub water green and cloudy? Low pH can allow copper to crowd the water and making it green and often times cloudy.
  • Do you need to drain green hot tub water? Most likely not, if it is related to imbalanced water levels.
  • Shock treat with non-chlorine Oxy Spa after each use to kill bacteria.
  • Test water chemistry weekly (biweekly with Cleanwater Blue) to maintain proper levels.
  • Drain and clean spa every 3 – 4 months.

Did you have green spa water and use one of these tips to clear it up?  Let us know how it worked in the comments below!


  1. Good read but I noticed that you never mentioned purging your hot tub. I believe this is essential to the well maintained hot tub. No matter what you do, if you have dirty plumbing, you will never get your water right.


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