Why Does My Spa Water Look Green?

One of the most annoying and persistent Hot Tub or Swim Spa issues is the appearance of green water, it can even happen in a Self-Cleaning Hydropool North West Hot Tub! It can be discoloured for a range of factors which will be discussed in this article.



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

Excessive Metal Content

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

Low Sanitiser Levels

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

Low Ph

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


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

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. 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.

For a more intense case of Algae:

1. 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. 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. 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. After flushing the plumbing & cleaning the spa shell and filter, refill the hot tub.

5. Test the water’s Total Alkalinity and pH, adjust to normal levels.

6. Use Spa Algaecide for weekly preventative measures as directed on bottle.


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


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 remove green water in your hot tub.

3. Retest water chemistry levels including sanitiser and adjust where necessary.

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

1. Use a hose end filter such as PreFresh to reduce metal impurities.

2. 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. Add Chitosan Natural Clarifier weekly, as preventative maintenance.

4. 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 sanitiser at all times is essential, life happens and spa maintenance can get left by the wayside for months. Shocking allows your sanitiser 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. 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 sanitiser.


1. Test water for sanitiser level.

2. Depending on sanitiser 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.


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! 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.


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.