How Do I Get Rid Of Mold & Mildew In And Around My Hot Tub?

Mold and mildew around a hot tub can be frustrating, unpleasant, and embarrassing. You open the cover expecting clean, relaxing water, but instead you notice a musty smell, dark spots, slimy residue, stained pillows, a dirty cover underside, or mildew growing around the cabinet, steps, cover lifter, or spa area. The good news is that most mold and mildew problems can be cleaned and prevented with the right approach.

Hot tubs naturally create warm, humid conditions. That moisture can collect under the cover, around seams, inside cabinet spaces, behind pillows, on steps, and in shaded areas around the spa. When moisture combines with body oils, lotions, old water, poor sanitizer levels, dirty filters, or trapped organic buildup, mold and mildew can develop more easily.

The key is to clean the visible growth, correct the moisture or water care problem that allowed it to form, and improve your regular maintenance routine so it does not keep coming back.

1. What Is The Difference Between Mold And Mildew?

Mold and mildew are both types of fungal growth, but they often look and behave a little differently. Mildew is usually more surface-level and may appear as white, gray, or powdery patches. Mold can appear darker, thicker, fuzzy, slimy, green, black, brown, or spotted, and it may be more difficult to remove if it has worked into porous materials.

• Mildew often grows on damp surfaces and may wipe away more easily.
• Mold may appear darker, fuzzy, slimy, or more stubborn.
• Both thrive in warm, damp, poorly ventilated areas.
• Both can return if the moisture problem is not corrected.

Why it matters: Cleaning the surface is only the first step. You also need to remove the moisture, residue, and water care issues that allowed mold or mildew to grow.

2. Where Mold And Mildew Commonly Show Up Around A Hot Tub

Mold and mildew can appear in several places around a spa. Some are easy to see, while others may be hidden behind panels, under the cover, or around damp accessories.

• Underside of the hot tub cover, especially if moisture and vapors are trapped.
• Cover seams and stitching, where water and residue collect.
• Spa pillows and headrests, especially behind removable cushions.
• Waterline and shell surface, where oils and residue accumulate.
• Filters and filter compartments, if cartridges are dirty or neglected.
• Cabinet panels and corners, especially shaded or damp areas.
• Steps, decking, and spa pads, where water drips and sits.
• Inside foam or insulation, if there has been a leak.

Helpful tip: If you smell mildew but cannot see it, check hidden damp areas: under the cover hinge, behind pillows, under steps, around the equipment bay, and inside any areas affected by leaks.

3. Why Mold And Mildew Grow Around Hot Tubs

Hot tubs create the conditions mold and mildew like: warmth, moisture, shade, and organic material. If the spa area does not dry well, if the cover stays damp, or if water chemistry is neglected, growth can happen faster.

• Warm water creates humidity under and around the cover.
• Low sanitizer allows organic buildup to remain in the water.
• Old water holds more dissolved contaminants.
• Dirty filters allow residue to circulate.
• Poor ventilation traps damp air.
• Leaks keep insulation, cabinets, or decking wet.

Bottom line: Mold and mildew are usually a sign that moisture, residue, or water care needs attention.

4. Start With Safety Before Cleaning

Before cleaning mold or mildew, protect yourself and the spa. Avoid harsh cleaning methods that can damage vinyl, acrylic, pillows, seals, covers, and plumbing. Also be careful around electrical components if moisture is present near the equipment bay.

• Wear gloves when cleaning mold or mildew.
• Use eye protection if spraying cleaner overhead or under the cover.
• Work in a ventilated area when using cleaners.
• Turn off power before inspecting wet equipment areas.
• Avoid mixing chemicals or cleaners.
• Test cleaners on a small area when unsure.

Important safety note: Never mix bleach with other cleaning products, especially ammonia-based cleaners. Mixing chemicals can create dangerous fumes.

5. Clean The Underside Of The Hot Tub Cover

The underside of the cover is one of the most common places for mildew because it is exposed to warm steam, chemical vapors, and trapped moisture. Cleaning it regularly helps prevent odor and buildup.

• Remove the cover from the spa if possible.
• Rinse loose residue with clean water.
• Use a spa-safe cover cleaner or mild cleaner recommended for vinyl covers.
• Wipe the underside with a soft cloth or sponge.
• Pay attention to seams, folds, and hinge areas.
• Rinse thoroughly so no cleaner residue remains.
• Let the cover dry before closing it again.

Helpful tip: Do not use abrasive pads, harsh solvents, strong bleach mixtures, or household cleaners that can dry out or damage the cover material.

6. Clean Spa Pillows And Headrests

Spa pillows are another common mildew area. Moisture can get behind the pillow, and residue can collect where the pillow touches the shell. If the pillow is removable, take it off and clean both the pillow and the area behind it.

• Remove pillows if the design allows it.
• Wipe the back side of each pillow.
• Clean the shell area behind the pillow.
• Inspect for cracks, swelling, or deterioration.
• Allow pillows to dry before reinstalling.
• Replace pillows that are cracked, sticky, peeling, or badly stained.

Helpful tip: Remove pillows when shocking the spa or making heavy chemical adjustments if your manufacturer recommends it. Chemical vapor can shorten pillow life.

7. Clean The Waterline And Shell Surface

Mold and mildew may not always grow directly in properly sanitized water, but residue at the waterline can still create a dirty, slippery, or unpleasant surface. Body oils, lotions, sunscreen, makeup, and detergent residue from swimsuits can form a ring where contaminants collect.

• Use a spa-safe surface cleaner.
• Wipe around the waterline.
• Clean around jets, pillows, filter openings, and corners.
• Avoid abrasive scrubbers that can scratch acrylic.
• Rinse or wipe away cleaner residue before soaking.

Helpful tip: A clean waterline reduces odor, foam, and residue that can transfer to the cover underside.

8. Clean Or Replace The Filter

A dirty filter can contribute to mold, mildew, odor, cloudy water, and poor circulation. Filters trap oils, debris, and fine particles. When the filter is clogged or greasy, contaminants remain in the water longer and can feed odor problems.

• Rinse the filter between pleats with a garden hose.
• Deep clean with a spa filter cleaner.
• Rinse thoroughly before reinstalling.
• Replace filters that are cracked, collapsed, greasy, or no longer rinse clean.
• Keep a spare filter if possible so one can dry while the other is in use.

Helpful tip: Do not clean spa filters in the dishwasher or with household soap. Heat and detergent residue can damage filters and cause foaming.

9. Balance The Water And Restore Sanitizer

Cleaning the visible mold or mildew is not enough if the water is out of balance. Low sanitizer, poor pH, unstable alkalinity, or old water can allow odors and residue to come back quickly. After cleaning surfaces, test and correct the water.

• Test sanitizer level.
• Test pH and alkalinity.
• Adjust alkalinity first if pH is unstable.
• Shock or oxidize according to product directions if needed.
• Allow water to circulate after treatment.
• Leave the cover open briefly after heavy chemical treatment when appropriate.

Helpful tip: If the water smells bad or sanitizer disappears quickly, the spa may have a larger organic buildup problem that requires deeper cleaning or a drain and refill.

10. Drain And Refill If The Water Is Old Or Contaminated

Sometimes fresh water is the best solution. If the spa water is old, foamy, smelly, cloudy, difficult to balance, or repeatedly causing mildew odor under the cover, it may be overloaded with dissolved contaminants.

• Drain if the water is several months old.
• Drain if odors return quickly after treatment.
• Drain if sanitizer demand is unusually high.
• Drain if foam, slime, or film keeps returning.
• Clean the shell before refilling.
• Start fresh with balanced water and clean filters.

Helpful tip: Fighting old water can cost more in chemicals and frustration than draining, cleaning, and refilling.

11. Use A Plumbing Purge If Biofilm Is Suspected

If the spa has a persistent musty smell, recurring slime, cloudy water, or sanitizer that disappears quickly, the issue may be inside the plumbing. Biofilm can develop in plumbing lines when organic material builds up over time. Surface cleaning alone will not remove buildup hidden inside pipes and manifolds.

• Use a spa plumbing purge product before draining.
• Follow the product directions carefully.
• Run pumps as directed to circulate cleaner through the lines.
• Drain after purging.
• Clean the shell and filter area before refilling.
• Install a clean or new filter after the purge.

Helpful tip: If mold or mildew smell keeps returning even after cleaning the cover and balancing water, hidden plumbing buildup may be part of the problem.

12. Check For Leaks Around The Spa

Mold and mildew around the cabinet, steps, deck, or spa pad may be caused by a leak rather than normal humidity. If water is constantly dripping from the spa or collecting under the cabinet, the area may never dry properly.

• Look for wet spots under the spa.
• Inspect pump unions and heater unions.
• Check drain caps and valves.
• Look for damp insulation or water trails inside the cabinet.
• Fix leaks before cleaning exterior mildew.
• Dry the area thoroughly after repair.

Helpful tip: If mildew keeps forming in one specific area near the base of the spa, inspect for a slow leak.

13. Clean The Cabinet, Steps, And Surrounding Area

Mold and mildew can grow outside the spa too, especially in shaded, damp areas. Steps, decks, mats, cover lifters, towel storage, and cabinet corners may stay wet after use. Cleaning the surrounding area helps prevent mildew from spreading back to the spa.

• Clean spa steps and textured surfaces.
• Wipe cabinet panels with a suitable cleaner.
• Move objects that trap moisture against the spa.
• Improve drainage around the spa pad.
• Trim plants or landscaping that blocks airflow.
• Allow towels, mats, and accessories to dry fully.

Helpful tip: Mildew often returns when damp accessories, towels, or mats are stored too close to the hot tub.

14. Improve Ventilation And Drying

Moisture control is one of the best ways to prevent mildew. If the cover, cabinet, steps, or surrounding area never dry, mildew is more likely to return. Better airflow can make a big difference.

• Open the cover briefly after chemical treatment when appropriate.
• Let the underside of the cover dry during cleaning.
• Keep the spa area from being boxed in too tightly.
• Allow steps and mats to dry.
• Avoid storing wet towels on or near the cover.
• Check that cabinet vents are not blocked.

Helpful tip: Mold and mildew prevention is not only about chemicals. Drying and airflow matter too.

15. When Cleaning Is Not Enough

Some parts cannot be fully restored once mold, mildew, moisture, or chemical damage has gone too far. A waterlogged cover, deteriorated pillows, soaked insulation, or badly contaminated filter may need replacement rather than repeated cleaning.

• Replace a cover that is heavy, waterlogged, cracked, or smells from inside.
• Replace pillows that are peeling, sticky, cracked, or deeply stained.
• Replace filters that remain greasy, smelly, or clogged after cleaning.
• Replace damaged gaskets or seals that trap residue or leak.
• Remove and replace wet insulation if a leak caused hidden mildew.

Bottom line: If the smell is inside the material, surface cleaning may not be enough. Replacement may be the cleaner and healthier long-term fix.

Quick Mold & Mildew Removal Checklist

• Wear gloves and avoid mixing cleaning chemicals.
• Identify where the mold or mildew is growing.
• Clean the underside of the cover with spa-safe cleaner.
• Remove and clean spa pillows if possible.
• Wipe the waterline, shell surface, and jet areas.
• Rinse and deep clean the filter.
• Test sanitizer, pH, and alkalinity.
• Shock or oxidize as needed according to product directions.
• Drain and refill if the water is old or smelly.
• Use a plumbing purge if biofilm is suspected.
• Check for leaks that keep the cabinet or area wet.
• Improve airflow and let cleaned parts dry fully.
• Replace waterlogged, cracked, or contaminated parts.

This checklist can help remove visible mildew and correct the conditions that allowed it to grow.

Common Mold & Mildew Mistakes To Avoid

• Only cleaning what you can see. Moldy smells may come from the cover, filter, plumbing, cabinet, pillows, or wet insulation.
• Using harsh household cleaners on spa surfaces. Strong chemicals can damage vinyl, acrylic, pillows, and seals.
• Ignoring water chemistry. Low sanitizer and poor balance allow odor and residue problems to return.
• Leaving the cover wet after cleaning. Trapped moisture encourages mildew to return.
• Keeping old filters too long. Dirty or deteriorated filters can hold odor and contaminants.
• Forgetting to check for leaks. Damp cabinets, steps, and insulation may point to a slow leak.
• Trying to save parts that are too far gone. Waterlogged covers, moldy foam, and deteriorated pillows may need replacement.

Avoiding these mistakes can help keep your spa cleaner, fresher, and easier to maintain.

Key Takeaways

• Mold and mildew grow where moisture, warmth, and organic residue collect. Covers, pillows, filters, waterline areas, cabinets, steps, and damp surroundings are common problem spots.
• Cleaning the surface is only part of the solution. You also need to correct water chemistry, improve filtration, reduce trapped moisture, and inspect for leaks.
• Spa-safe cleaning matters. Harsh household cleaners can damage vinyl covers, acrylic shells, headrests, seals, and spa surfaces.
• Old water and dirty filters make odor problems worse. Drain and refill when water becomes overloaded, and clean or replace filters on schedule.
• Some parts need replacement. Waterlogged covers, deteriorated pillows, smelly filters, or wet insulation may not be fully fixable with cleaning alone.

Getting rid of mold and mildew around a hot tub requires a complete approach. Clean the visible growth, but also test and balance the water, clean the filter, inspect the cover, check hidden damp areas, and improve airflow. If the odor or growth keeps coming back, look deeper for old water, biofilm in the plumbing, a slow leak, or parts that are holding moisture inside.

With consistent cleaning, balanced water, dry surfaces, and good ventilation, your hot tub area can stay fresher, cleaner, and more inviting. And when a cover, pillow, filter, or insulation is too far gone, replacing the damaged part is often the best way to stop the problem from returning.