Clean, clear hot tub water doesn't happen by accident. Because a spa contains a relatively small amount of warm water and may have several people using it at once, water chemistry can change much faster than it does in a swimming pool.
The key is a consistent routine: maintain proper water balance, keep an effective sanitizer residual, provide adequate filtration and circulation, clean the filter, and replace the water when necessary.
These seven steps can help you keep your hot tub water clean, comfortable, and easier to maintain.
1. Test Your Fill Water & Calcium Hardness
Before trying to balance a freshly filled hot tub, it helps to understand the water going into it.
Calcium hardness measures the amount of dissolved calcium in the water. Water with too little calcium can contribute to aggressive or corrosive water conditions, while excessive calcium hardness can contribute to scale formation and cloudy water.
A calcium hardness level around 200–400 ppm is commonly considered an ideal water-balance range, although the correct range can vary depending on the hot tub, surface, equipment, sanitizer system, and manufacturer's recommendations.
Test your fill water before adding calcium increaser. If the water already contains substantial calcium, adding more may create unnecessary scale problems.
If calcium hardness is unusually high, simply adding another chemical may not solve the underlying problem. Depending on the source water, partial replacement with lower-hardness water or other water-treatment methods may be appropriate.
2. Balance Total Alkalinity & pH
Total alkalinity and pH work closely together and are two of the most important measurements in hot tub water care.
pH measures how acidic or basic the water is. A commonly recommended spa range is approximately 7.2–7.8.
Total alkalinity helps buffer the water against rapid changes in pH. A commonly targeted range is approximately 80–120 ppm, although the appropriate range can vary with the sanitizer and water-care system.
Water that is too acidic can contribute to corrosion, equipment damage, and swimmer discomfort. Water with excessively high pH can contribute to scale, cloudy water, and reduced sanitizer effectiveness.
When adjustment is necessary:
- Test both pH and total alkalinity before adding chemicals.
- Generally address significant alkalinity problems before fine-tuning pH.
- Add only the amount recommended for your spa's actual water volume.
- Allow the water to circulate according to the chemical manufacturer's instructions.
- Retest before making another large adjustment.
Avoid repeatedly adding chemicals based on guesswork. Small, measured adjustments are usually easier to control than attempting to correct the entire water balance at once.
3. Choose & Maintain the Proper Sanitizer
A sanitizer is essential because warm spa water provides an environment where microorganisms can multiply rapidly if the water is not properly treated.
The two most common primary sanitizers used in residential hot tubs are chlorine and bromine.
Chlorine
Chlorine is a fast-acting and widely used spa sanitizer. For hot tubs, products specifically labeled for spa use should be used according to their directions.
Dichlor is commonly used in spas because it dissolves quickly. Products intended primarily for swimming pools, including some slow-dissolving trichlor tablets, should not automatically be used in a hot tub. They may have different chemical characteristics and may not be approved by the spa manufacturer.
A commonly recognized free available chlorine range for spas is approximately 2–5 ppm, but always follow the sanitizer label and hot tub manufacturer's recommendations.
Bromine
Bromine is another popular hot tub sanitizer and tends to remain effective over a relatively broad range of spa conditions.
A commonly recognized total bromine range for spas is approximately 4–6 ppm.
Bromine systems can use tablets in an appropriate feeder or dispensing system, or may use sodium bromide as part of a bromine-generating water-care program.
When sodium bromide is used, it must be properly activated according to the water-care system instructions to create an active bromine sanitizer residual.
Mineral Systems
Mineral cartridges and similar products can be used with certain spa water-care systems to supplement water treatment.
They should not automatically be considered a replacement for chlorine, bromine, or another approved primary sanitizer. Follow the instructions for the particular mineral system to determine what sanitizer residual must still be maintained.
Ozone Systems
Many hot tubs are equipped with an ozonator. Ozone can help oxidize contaminants as water passes through the spa's circulation system and can reduce the workload placed on the primary sanitizer.
An ozonator should generally be considered supplemental water treatment, not a replacement for maintaining the appropriate sanitizer residual in the spa water.
Ozone systems also require maintenance. Ozone output decreases over time, so an older ozonator may appear to be operating even though its ozone production has diminished significantly.
4. Control Scale, Metals & Staining
Fill water can contain calcium, iron, copper, manganese, and other dissolved minerals that may contribute to scale, staining, or water discoloration.
If your source water contains significant metals or you routinely experience scale, an appropriate stain-and-scale control product may help. However, these products should be used based on your water conditions rather than automatically added to every spa on a fixed weekly schedule.
Proper pH, alkalinity, and calcium hardness are also important because water that is out of balance can accelerate scale formation or corrosion.
If you repeatedly experience staining, scale, or unusually colored water immediately after filling the spa, testing the source water can help identify the underlying cause.
5. Keep the Water Clear by Fixing the Cause
Cloudy hot tub water is usually a symptom rather than the actual problem.
Common causes include:
- Low sanitizer levels
- Heavy bather load
- Dirty or clogged filters
- Insufficient circulation
- Improper pH or alkalinity
- Body oils, lotions, cosmetics, and other organic contaminants
- Old water with excessive dissolved contaminants
A spa clarifier can sometimes help the filter capture very small suspended particles, but clarifier should not be used to hide an underlying sanitation or filtration problem.
Enzymes
Spa enzymes may help break down certain organic contaminants such as body oils and lotions and can help reduce waterline buildup.
Clarifiers
Clarifying products can cause very small suspended particles to group together so the filter can capture them more effectively.
These products can be useful when appropriate, but properly balanced and sanitized water with an effective filtration system should not necessarily require routine clarifier use.
6. Clean & Replace Your Hot Tub Filter
The filter is one of the most important parts of your hot tub's water-care system. It continuously removes particles and contaminants from the water as the circulation system operates.
A dirty filter can reduce water flow, make the heater and circulation system work harder, and make clear water much more difficult to maintain.
Remove the cartridge periodically and rinse thoroughly between the pleats. Spa filters exposed to body oils, lotions, and other contaminants also benefit from periodic deep cleaning with an appropriate cartridge-filter cleaner.
Our Spa & Pool Filter Cartridge Cleaning Guide provides step-by-step instructions for properly cleaning a cartridge filter.
Filters do not last forever. Replace the cartridge when the filter media becomes damaged, the end caps crack, the pleats deteriorate, or cleaning no longer restores adequate water flow.
Use our Filter Finder to search by filter part number, hot tub manufacturer, model, cross-reference number, or cartridge measurements.
If the original filter number is no longer readable, the measurement finder can help identify replacement cartridges using the filter's outside diameter, length, openings, and end-cap styles.
7. Keep the Hot Tub Covered When It Isn't Being Used
A properly fitted hot tub cover does much more than conserve heat.
Keeping the spa covered when it is not in use can:
- Reduce leaves, dirt, insects, and debris entering the water
- Reduce water evaporation
- Help maintain water temperature
- Reduce unnecessary sanitizer loss
- Help protect the spa from outdoor contaminants
Keep the cover clean and inspect it periodically for cracks, torn seams, damaged straps, waterlogging, or deterioration.
Don't Forget Periodic Water Changes
Even perfectly maintained hot tub water eventually needs to be replaced.
Every time the spa is used, bathers introduce perspiration, body oils, lotions, cosmetics, and other contaminants. Chemicals and dissolved minerals also accumulate over time as water evaporates and is replaced.
Many residential hot tubs are drained and refilled approximately every three to four months, although heavily used spas may require more frequent water changes.
If the water becomes increasingly difficult to balance, repeatedly foams, develops persistent odors, or no longer responds normally to sanitizer and filtration, replacing the water may be more effective than continuing to add chemicals.
A Simple Hot Tub Water-Care Routine
You don't need to constantly add products to maintain clean spa water. A consistent maintenance routine is more important.
- Test sanitizer and pH regularly.
- Maintain proper total alkalinity and calcium hardness.
- Keep the circulation and filtration system operating properly.
- Clean the filter on a regular schedule.
- Maintain an appropriate sanitizer residual.
- Oxidize or shock the water when required by your water-care program.
- Keep the spa covered when not in use.
- Drain, clean, and refill the spa periodically.
The exact products and chemical levels required can vary by hot tub manufacturer, sanitizer system, source water, spa usage, and local water conditions.
Bath & Spa Parts Online has been helping customers maintain and repair hot tubs, spas, pools, and bath systems for more than 45 years.
Visit our Knowledge Base for additional maintenance guides, troubleshooting information, replacement-part resources, and our specialized part finders.
If you need help identifying a replacement part, give us a call at 800-918-9143.
Always follow your hot tub manufacturer's water-care recommendations and the directions printed on chemical product labels. Never mix concentrated pool or spa chemicals together.