Why is my hot tub water green - Sutro, Inc

Why is my hot tub water green

Green water in a hot tub is an unpleasant sight and the root of other upcoming problems, such as a clogged circulation system. If you have green water in your hot tub, it may be a sign of negligence towards maintenance.

The best is to identify why the water is green and treat it as quickly as possible. You must also follow some preventive measures to fix the problem in the bud.  

Why is your hot tub water green? 

The green color of your hot tub water can have three primary sources. Here is how you can identify them:


It is one of the biggest causes of green water in hot tubs and swimming pools. Algae is a microorganism, a small aquatic plant that can build up overnight in a hot tub.

The chances of finding algae in an outdoor hot tub fitted with a cover are low but never zero. 

Detecting algae in a hot tub is easy. When you find the water greenish and cloudy, rub your palms against the tub walls. If you feel a slimy touch, it is algae for sure. 

Dissolved metals/minerals

Sometimes, adding an oxidizer to the hot tub water causes a reaction with metals already in the water. While different metals react to produce different colors, the greenish tinge is a result of copper reacting with the oxidizer. 

These metals/minerals can come from the water source used to fill the hot tub or through the components (such as copper fittings) and accessories.  

Maintenance Issues

In minor algae infestations, people sometimes add sanitizer and algaecide to the water but do not clean the insides. While the water may lose its greenish color and look clean, the filters and plumbing still have algae, bacteria, and mold sticking to it. 

A dysfunctional or dirty filter can also be a cause if the greenish water is a recurring menace in your hot tub. 


How do you fix it? 

These are the best fixes for treating green hot tub water: 

For Algae 

Algae growth in your hot tub can be at minor or significant levels. The process is similar to treating algae in a pool. Hard shock the water and use an algaecide to curb its growth. 

Either way, you must follow a thorough process of elimination to ensure cloudy water does not become a regular episode for your tub. Here's the step-by-step procedure for this:

  1. The objective here is to clean your hot tub. Start with draining the tub and giving the insides a thorough cleaning. We recommend a complete drain of water. 

  2. Pull out the filters and clean them. You can also refer to our guide on how to clean hot tub filters.

  3. Perform a hot tub flush to purge algae/bacteria residues inside the plumbing.

  4. Scrub the inside wall of the hot tub using an appropriate hot tub cleaner. Avoid using any household remedy (white vinegar, bleach, etc.) as it can damage hot tub walls, cause foaming, or alter water balance.

  5. Flush the plumbing, reinstall the filters, and fill the hot tub with water.

  6. Check the water chemistry, especially the pH, total alkalinity, and sanitizer levels. Set them back to normal levels using the appropriate hot tub chemicals. Balance alkalinity before the pH.

Note: Please wash and dry the hot tub cover thoroughly with a 1:1 bleach-water solution before putting it back on. 

For Minerals and Metals  

If the greenish problem is due to the onset of metal contaminants, you should use a sequestering agent that will remove any heavy metals from the water. 

How can you prevent it from coming back? 

Congratulations! Now that you have treated the problem of green water in your hot tub, it is time to take some preventive measures. 

The process of dealing with algae can be tedious, and you must consider these factors to avoid it:

Keep it Covered

Always cover a hot tub situated outdoors. That's because algae spores and other bacteria come floating in the air. Plus, elements (leaves, dirt, etc.) can also contaminate the water. 

Regular Testing and Maintenance

You must check the water chemistry regularly so you don’t miss any significant changes. Check the sanitizer (chlorine) levels daily, the pH and alkalinity test must be done twice or thrice a week. 

Add chemicals when needed, and clean the filtration system regularly. 

You can use pool test strips, liquid test kits, or a simple alternative like a hot tub monitor. For example, our Sutro Hot Tub Water Monitor is a battery-operated device that sits submerged inside your hot tub and delivers real-time updates of water chemistry on the mobile app. 

Maintain Hygiene 

Always use clean swimwear before entering your hot tub, shock the hot tub after heavy use, and keep pets away from the hot tub. Using oils, lotions, and other body care products will also contaminate the water. 

The Garden Hose

An often overlooked cause of green water in your hot tub is the garden hose used to fill it up. An unclean hose can already have algae or mold buildup inside. It is best to use a clean hose with a pre-filter.


Green water in a hot tub can be due to algae growth, metal contamination, or an unclean water source. Cleaning the hot tub, maintaining proper water chemistry, and following maintenance procedures are the best way to counter it.

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