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.

Troubleshooting Green Hot Tub Water

| Algae Making Hot Tub Water Green

Algae growth in a hot tub is accompanied by a slimy coating on the inside of the spa. Algae comes in many different colours, such as black, mustard, or white. 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.

Removing Algae From Your Hot Tub:

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 Removal Of Persistent Hot Tub Algae:

1. Perform a full Spa 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 spa flush product, drain and clean inside of spa with Surface Cleaner 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 (read how in our free Maintenance Guide) or replace the filter cartridge, especially if it is more than 1 year old. Replace with new filter(s) or cleaned filter(s). 

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 with additional sanitiser if needed.

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

| Excessive Levels Of Metals Making Hot Tub Water Green

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.

How To Remove Excessive Metal Content From Hot Tub Water:

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 a CuLator SpaPak to filter/skimmer area. You could also use any other Metal Sequestrant - these vary in name but can be found as "Metal Klear" or Stain and Scale Remover.  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 to reduce metal impurities. 

2. Add a Metal Sequestrant as directed on bottle to remove the spa of stain-causing metals such as copper, that the hose filter did not catch.

3. Add Spa Sparkle weekly, as preventative maintenance.

4. Use non-chlorine shock after each use to maintain healthy spa water.

5. Add CuLator SpaPak to filter/skimmer area.

| Low Sanitiser Levels Making Hot Tub Water Green

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 Rapid Shock or a Non-Chlorine Shock. 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.

Raise Low Sanitiser Levels To Get Rid Of Green Hot Tub Water

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.

| Low pH Levels Making Hot Tub Water Green

Low pH water is acidic. When the water in your spa becomes acidic (meaning the pH level is too low, ideally it should be between 7.4 and 7.6), it actually becomes corrosive. This corrosive water aggressively starts dissolving soft metals, especially copper, which is often used in spa heating elements and sometimes in plumbing components. When this dissolved copper reacts with your sanitiser (like chlorine) through a process called oxidation, it chemically turns the water that distinct greenish-blue colour. So, while low pH itself doesn't turn the water green, the acidity corrodes metals in the equipment, and that release of copper into the water is what causes the green tint. It's a key sign that your water chemistry is attacking your internal components, which is why balancing the pH is so vital for maintaining your luxury hot tub here in the North West.

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.

How To 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 hot tub water.

We understand that tackling green water can feel overwhelming, but by methodically testing, identifying the cause (whether it's algae, metals, or off chemicals), and applying the right products, you can quickly restore your spa's brilliant clarity and ensure perfect hot tub water quality. Remember, preventative maintenance is always the easiest solution!

Should you find yourself needing hands-on help, or if you simply want to free up your time for more relaxation, our highly-rated Hydropool North West Services team is here for you. Serving Greater Manchester and North Wales, we offer everything from chemical guidance and filter cleaning to full-system flushes, ensuring your Hydropool luxury hot tub remains a source of stress-free enjoyment. Give us a call—we’re always happy to help you keep your spa water pristine!