Spas, hot tubs and whirlpools operate with significantly smaller water volumes than traditional swimming pools while often experiencing a much higher bather load. The elevated water temperature, typically 35–40°C, also creates favourable conditions for bacterial growth if water quality is not carefully controlled.
Common Issues
- Cloudy Water
- Unpleasant Odours
- Biofilm in Pipework
- High Bacterial Load
- Rapid Organic Build-up
- Incorrect pH or Disinfectant Levels
Common Treatment Methods
- Cartridge Filters
- Sand Filters (larger systems)
- Chlorine or Bromine
- UV Disinfection
- Ozone
- Regular Water Replacement
High Temperature Requires Extra Attention
The elevated temperature in spas and hot tubs allows bacteria and biofilm to develop faster than in conventional swimming pools. Regular monitoring of disinfectant levels, pH and filter performance is therefore especially important.
Common Chlorine Dosing Methods
Chlorine can be added in several different ways depending on the size and application of the system. Smaller pools and spas often use chlorine tablets, while larger facilities typically rely on automatic dosing systems. An increasingly popular solution is saltwater pools where chlorine is generated directly in the water using an electrolytic cell.
- Chlorine Tablets – simple and common for residential pools and spas.
- Liquid Chlorine Dosing – commonly used in larger and commercial systems for accurate control.
- Saltwater Chlorinator – an electrolytic cell converts dissolved salt (sodium chloride, NaCl) into free chlorine that disinfects the pool water. Despite the name, most saltwater pools contain far less salt than seawater.
Many spas use bromine instead of chlorine. Bromine generally performs well at the elevated temperatures found in spas and hot tubs, while chlorine remains the most common disinfectant in conventional swimming pools.
Benefits of UV and Ozone
- Can Reduce Bacteria and Viruses
- Can Reduce Chloramines
- Can Improve Odour and Water Quality
- May Reduce Water Replacement Frequency
- May Improve User Comfort
Limitations
- UV and Ozone Do Not Normally Fully Replace Chlorine or Bromine
- Small Water Volumes Change Quickly
- Regular Maintenance is Required
- Filters Require Regular Cleaning
Example Treatment Trains
Spa
↓
Cartridge Filter
↓
Chlorine or Bromine
↓
Spa
Spa
↓
Filtration
↓
UV Disinfection
↓
Chlorine or Bromine
↓
Spa
Spa
↓
Filtration
↓
Ozone
↓
Chlorine or Bromine
↓
Spa
Due to elevated temperatures and often high bather loads, spas and hot tubs generally require more frequent monitoring and maintenance than traditional swimming pools. UV and ozone systems can significantly improve water quality, but should typically be considered a complement to chlorine or bromine rather than a complete replacement.