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Guaranteeing a perfect pool and water spa experience is one of pool operators’ key priorities. While cloudy water can become a challenge, it can be addressed by following expert advice for maintaining hot tubs.

What causes cloudy water in hot tubs and how can this be avoided to ensure your pool has the best aspect and quality?

In this article, will be covered:

  • What we mean by cloudy water;
  • Main causes of cloudy water in hot tubs;
  • How to avoid this phenomenon in your hot tub.
What is cloudy water?

Cloudy water is a term used to describe water that looks murky, resulting in an unsightly appearance. Usually, in this scenario one cannot see the bottom of pools with cloudy water because tiny particles have mixed in with the water and, in large numbers, they reflect the surrounding light.

The particles within cloudy water range from 0.5 to 5 microns, so they are impossible to spot with the naked eye. They normally appear due to an imbalance in the water chemicals, poor filtration, or other environmental factors.

Of course, the main concern with cloudy water in hot tubs is that they cause the water to look unappealing, followed by more serious underpinning problems related to pool hygiene. This is why you should find the underlying cause of cloudy water and address it immediately.

What causes cloudy water in hot tubs?

There are seven main causes that lead to cloudy water being formed, ranging from improper level of pH to algae formation, among others.

  • Inadequate pH and chlorine levels

An imbalance in pH renders the free chlorine ineffective, with too little forming chloramine. Combined with chlorine, this makes the water look murky.

Combined chlorine levels need to be below 0.5 ppm or just under 0 ppm, with optimal pH levels between 7.2 and 7.6.

Water with high pH (above 7.8) also renders chlorine ineffective against bacteria, further affecting the water quality and risking growth of algae.

  • Ammonia

Ammonia is one of the most common pool pollutants, brought into the water by people or by the environmental conditions. This simple chemical is produced naturally and bodily fluids like sweat or urine, skin flakes, as well as environmental particles brought in by the wind or rain, or even skin care products all can bring it into the water.

  • Early stages of algae development

Algae multiply rapidly on warm, sunny days. Their spores enter the water from wind, rain, swimsuits, or even pool cleansing tools. If there is no accurate filtration and water recirculation, or if the pool has low free chlorine levels, nitrates or CO2 in warm environments, then algae will begin to grow.

  • Hard water (high calcium levels)

Calcium hardness (CH) refers to the sum of all calcium dissolved in water. High levels are unstable, and are further affected by pH imbalance and total alkalinity (TA). CH levels should be in the 100-400 ppm range and are temperature dependent. At above 400 ppm, you will notice cloudiness and calcium scaling.

  • Alkaline imbalance

Total alkaline levels need to be kept low to prevent cloudy water from occurring. Otherwise, a pH imbalance and calcium scaling will occur.

  • Faulty or clogged filters

Your hot tub needs to have a well functioning filter to prevent it from becoming cloudy or dirty. 90% of cloudy pools are caused by faults with the filtration system.

  • Debris

Environmental debris including leaves, twigs, flowers, etc. will affect water quality, especially when water isn’t recirculated properly. Even dust or pollen can build up in the filter and affect water appearance.

How to avoid cloudy water formation

The main ways to avoid cloudy water in hot tubs involve addressing the 7 causes mentioned above:

  • Balance free chlorine levels;
  • Eliminate excessive ammonia;
  • Remove young algae;
  • Ensure correct calcium hardness levels;
  • Monitor and balance pH and TA levels;
  • Backwash filter or replace filtering agent;
  • Remove foreign particles and mineral deposits, scrub and vacuum up the pool.


First step: take a free chlorine reading and balance it

As one of the most common causes of cloudy water is low free chlorine levels, start by measuring this in your hot tub. You can then calculate the value of combined chlorine by subtracting free chlorine from total chlorine values. If free chlorine is below 3 ppm, or combined chlorine above 0.5 ppm, chlorinate your pool immediately.


Investigate ammonia and/or algae

Even after adding chlorine, free chlorine levels will not rise easily. If this continues after adding a large amount, you may have ammonia in the pool.

Perform an overnight chlorine loss test by adding chlorine after sunset and taking your free chlorine reading in the morning. If this is below 1 ppm through the night, this suggests you have algae starting to grow.

Ammonia and algae come about from insufficient free chlorine levels, so ensure these are always high enough to combat them.


Using algaecide to clear cloudy water

Although algaecide may clear out young algae, the best way to remove them is to scrub and clean the hot tub using a large leaf net, vacuum, and a liquid chlorine shock. Algaecide should be used sparingly as a preventive measure. When you have a full-on outbreak, however, it will be less useful. You may also end up using a large amount, spending a lot and getting worse results than through a liquid chlorine shock.


Remedy low free chlorine that has caused cloudy water

Low levels of free chlorine are caused by heavy usage, heavy rainfall or hot sunny days when UV light oxidises the pool. Using a chlorine stabiliser such as cyanuric acid prevents depletion caused by UV, but it is very strong and will cause free chlorine to disappear if it exceeds the recommended levels.

Liquid chlorine or sodium hypochlorite is the best option for a daily free chlorine boost, as it does not affect pH, calcium hardness and cyanuric acid levels in the water.


Monitor pH and total alkalinity

The pH levels affect how all other chemicals function in the water, therefore it is important to monitor them. High pH renders chlorine ineffective and makes water look dull, so ensure you keep pH between 7.4 and 7.8.

Total alkalinity should be in the range of 80-120 ppm to avoid raising pH levels and calcium scaling.


Clean the filtration system

Poor water circulation also leads to problems, so ensure that the return fittings are turned to point down, enabling water in the hot tub to circulate properly.

Make sure you use the right pump size and that the filtration system is running long enough. Remove any particles blocking the filter to keep water clean.


Remove foreign particles and deep clean the pool

You can use nets to remove visible particles and a pool clarifier to clear up the water if cloudiness persists. To remove fine particles, use a pool flocculant and vacuum the hot tub. To remove algae, scrub and clean the hot tub using a large leaf net and vacuum.

Keeping your hot tub free of cloudy water

Following the advice on how to treat the various causes of cloudy water in hot tubs will help to prevent this unsightly phenomenon. Additionally, a number of water treatment systems and applications can be deployed to make some of these processes automatic and reduce the burden of manual activity.

Some examples are:

  • Freepool2. A revolutionary solution for the treatment and disinfection of public swimming pools that uses neolysis to disinfect water with UV light and low salinity electrolysis;
  • Neolysis: The combination of UV technology with low salinity electrolysis in a single reactor has proven to be an excellent solution for the treatment and disinfection of swimming pool water. The Neolysis system combines the key features and benefits of these technologies and it corrects their drawbacks or limitations.
  • Fluidra Connect. A smart solution for supervising and controlling the pool remotely, enabling pool operators to activate the filtration, water treatment systems, pool lighting, irrigation systems, water jets, pool covers, and heating and dehumidifying systems.
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