Hot Tub Water Chemistry Guide

Water hardness is determined by the calcium level in the water. Too much calcium can contribute to scaling and excessive foaming, while too little calcium can make water more aggressive toward spa components.

• Fill your hot tub or spa.
• Use a test strip while the water is still cool.
• Add calcium increaser if the calcium level is too low.
• Wait 2 to 3 days before retesting.
• If too much calcium increaser was added, drain 6 to 12 inches of water, refill, and retest.
• If your source water has too much calcium, consider using softened water or keep pH and alkalinity balanced while using a mineral protection product.

Balanced water helps protect spa components, improves sanitizer performance, and helps prevent scaling, corrosion, cloudy water, and skin irritation.

• Use a test strip to measure pH and alkalinity.
• Correct alkalinity first while running the pump on high.
• To raise alkalinity, use an alkalinity increaser and follow the product instructions.
• If alkalinity is in range but pH is low, add pH increaser in small amounts, wait 30 minutes, and retest.
• To lower alkalinity or pH, use the appropriate reducer and retest after circulation.
• If alkalinity is very high and pH is below 7.0, drain 6 to 12 inches of water, refill, and retest.

Chlorine

Chlorine is fast acting and can help correct aggressive water problems. Dichlor is typically recommended for hot tubs because it dissolves quickly. Avoid using pool chlorine products in hot tubs unless your spa manufacturer specifically allows it.

Bromine

Bromine is commonly used in hot tubs because it does not evaporate as quickly as chlorine. It can be added using tablets in a floating dispenser or through systems designed to hold bromine tablets.

• Bromine tablets are one of the easiest methods and are commonly used with a floating dispenser.
• Sodium bromide is a two-step process that must be activated with an oxidizer such as chlorine or non-chlorine shock.

Mineral Cartridges

Mineral cartridges can be installed in the filter or used in a floating dispenser. Most cartridges last up to three months and are typically used along with chlorine, bromine, or non-chlorine shock.

Ozone

Ozone is a powerful oxidizer that helps reduce contaminants in the water. Many hot tubs include an ozonator that feeds ozone gas into the water. Ozonators should not be used on indoor spas unless properly vented, and they are designed to work with another sanitizer.

Some local water supplies contain higher levels of iron, copper, calcium, or other minerals. These can contribute to staining, heater damage, discolored water, and increased sanitizer demand.

Add a stain and scale control product weekly as a preventative measure, and test your water to determine the correct amount to use.

Hot water can encourage bacteria growth and can cause water to become cloudy or discolored if contaminants are not controlled. Adding a clarifier when you first fill the hot tub can help prevent cloudy water.

• Natural enzyme clarifiers help break down organics and contaminants, reduce scum lines, and minimize oily buildup without creating extra work for the filter.
• Synthetic coagulants bond small particles into larger particles that can be captured by the filter, but they may affect water chemistry.

Cleaning and replacing your cartridge filter is an important part of maintaining clean and healthy water. A dirty or worn filter can reduce water flow and make it harder to keep water clear.

View our Filter Cartridge Cleaning Guide for more information on cleaning your cartridge, or use our Filter Finder to locate a replacement filter.

A properly fitted hot tub cover helps keep water cleaner, reduces evaporation, helps retain heat, and supports a safer water environment when the spa is not in use.