How To Clean A Hot Tub That Has Been Sitting – Restore Your Spa
We have all been there. You uncover your spa after a long winter or a busy season only to find murky water and a strange smell. It is a common challenge for homesteaders and weekend warriors alike.
Learning how to clean a hot tub that has been sitting is the only way to ensure your soak is safe and sanitary. Stagnant water is a breeding ground for bacteria and biofilm that can ruin your equipment and your health.
This guide provides a step-by-step roadmap to deep cleaning your tub, purging the internal plumbing, and balancing the chemistry. You will go from a swampy mess to a crystal-clear oasis in just one weekend.
Table of Contents
Evaluating the Damage: Is Your Stagnant Spa Safe?
Before you grab the garden hose, you must assess the current state of the water and the shell. Stagnant water often hides biofilm, which is a slimy layer of bacteria that clings to the inside of your pipes.
Check for visible mold or “white water mold” which looks like shredded tissue paper floating in the water. If the water is dark green or black, you are dealing with significant organic growth that requires a heavy-duty approach.
Inspect the cabinet and the electrical components for signs of rodents or pests. Off-grid explorers and homesteaders often find that mice love the warmth of hot tub insulation during the colder months.
Ensure the GFCI breaker is functioning correctly before you touch the water or the controls. Safety is the first priority when dealing with a machine that combines electricity and water after a long period of neglect.
How to Clean a Hot Tub That Has Been Sitting the Right Way
The biggest mistake people make is simply draining and refilling the tub. If you do not clean the internal plumbing, the new water will be contaminated within hours by the gunk hidden in the lines.
Start by adding a line flush product to the old water before you drain it. These specialized chemicals circulate through the jets and break down the sticky biofilm that regular chlorine cannot reach.
Run the jets on high for at least thirty minutes, or follow the specific instructions on your flush product. You might see a thick, brown foam rise to the surface, which is a sign the cleaner is working.
Once the lines are purged, you can begin the physical cleaning process. Understanding how to clean a hot tub that has been sitting requires patience during this chemical breakdown phase to ensure a long-lasting result.
Essential Supplies for a Deep Clean
Gather your gear before you start so you do not have to stop mid-process. You will need a few specific items to handle the heavy lifting of a deep restoration.
- Line Flush Cleaner: To remove internal pipe gunk.
- Submersible Pump: This drains the tub much faster than the built-in gravity drain.
- Wet/Dry Vacuum: Essential for sucking out the last bit of water from the pipes and footwell.
- Non-Abrasive Sponge: A microfiber cloth or a dedicated spa mitt works best.
- pH-Neutral Shell Cleaner: Avoid household soaps, which cause massive foaming later.
- New Filter Cartridges: It is usually better to replace old filters than to try and save them.
If you are an RVer or living off-grid, ensure you have a pre-filter for your hose. This helps remove minerals and metals from your water source before they ever enter your spa.
Using the right tools prevents damage to the acrylic shell. Never use a stiff-bristled brush or abrasive scouring pads, as these create tiny scratches where bacteria can hide.
Step 1: The Plumbing Purge
As mentioned, the purge is the most critical step for a tub that has been sitting. Remove the filters before adding the purge chemical to prevent them from getting clogged with the dislodged debris.
Open all the jets and air valves to ensure the cleaner reaches every corner of the plumbing system. If your spa has a waterfall or neck jets, make sure those are running as well.
Let the solution circulate for several hours or even overnight if the tub has been sitting for more than six months. This gives the enzymes enough time to eat through stubborn organic matter.
Step 2: Draining the Swamp
Turn off the power at the circuit breaker before you begin draining. Running the pumps without water will cause them to overheat and potentially fail, leading to expensive repairs.
Use your submersible pump to empty the shell. Direct the old, chemically treated water away from your garden or lawn, as the high concentration of cleaners can harm plants.
Once the water level is low, use your wet/dry vacuum to pull the remaining water out of the jet lines. This is a pro trick that prevents old, dirty water from mixing with your fresh fill.
Wipe down the bottom of the tub to remove any sediment or “grit” that settled while the tub was sitting. This grit can act like sandpaper if it gets into your pump seals.
Step 3: Scrubbing the Shell and Cover
Spray your spa shell cleaner onto the acrylic and let it sit for a few minutes. Focus on the waterline, where oils and minerals tend to form a hard ring.
Use your microfiber cloth to scrub the entire surface, including the headrests and the underside of the cover. The cover is a major source of reinfection if it is not cleaned properly.
Rinse the shell thoroughly with fresh water and vacuum out the rinse water. Any soap residue left behind will create a “bubble bath” effect once you refill the tub and turn on the air blowers.
Inspect the cover for any tears or waterlogging. If the cover feels extremely heavy, the foam core is likely saturated with bacteria-filled water and should be replaced immediately.
Step 4: Filter Maintenance and Replacement
Your filter is the lungs of your hot tub. If the tub has been sitting, the filter is likely packed with dried-on contaminants that are nearly impossible to wash away.
While you can try using a filter soak overnight, we recommend starting with a fresh set of filters. This ensures your new water stays clean and your pump does not have to work overtime.
If you choose to clean the old ones, use a high-pressure hose nozzle to spray between every pleat. Do not use a pressure washer, as the intense force can tear the delicate filter fabric.
Check the filter housing for any debris or small stones. A clean housing ensures that the water flows freely and the filtration cycle remains efficient.
Step 5: Refilling with Fresh Water
Place your garden hose into the filter well rather than just dropping it into the footwell. This helps prevent air locks by pushing air out of the plumbing as the tub fills.
If you are using well water or have high metal content, use a hose-end pre-filter. This small investment saves you hours of work trying to balance chemistry later on.
Fill the tub until the water level is about an inch above the highest jets. Do not overfill, as the water level will rise once people get in, potentially overflowing into the cabinet.
Once filled, turn the power back on and check the control panel for any error codes. Listen for any strange grinding noises from the pumps that might indicate a mechanical issue after the long hiatus.
Chemical Startup for a Long-Sitting Tub
Now that the tub is full, you cannot just jump in. The water needs to be “shocked” to kill any remaining microscopic pathogens that survived the cleaning process.
Start by testing the Total Alkalinity (TA) and pH levels. It is much easier to balance the pH once the alkalinity is in the correct range (80-120 ppm).
Add a heavy dose of sanitizer, such as chlorine or bromine granules. For a tub that has been sitting, a “super-chlorination” or shock treatment is necessary to reach “breakpoint chlorination.”
Keep the cover off for at least 20 minutes after shocking the water. This allows the chemical gases to escape, which prevents the underside of your cover from deteriorating prematurely.
Test the water again after 24 hours. You want your sanitizer levels to be stable and your water to be perfectly clear before anyone takes a soak.
Troubleshooting Common Post-Sitting Issues
Sometimes, even after knowing how to clean a hot tub that has been sitting, you might encounter technical glitches. These are common when machinery sits idle for months.
If the jets are not blowing water but you hear the pump running, you likely have an air lock. You can often fix this by loosening the union nut on the discharge side of the pump until a little water trickles out.
If the heater is not working, check the “high-limit” switch. This is a safety reset button usually found on the heater assembly that can trip if the unit gets too hot or the flow is restricted.
Cloudy water shortly after refilling usually means the pH is too high or there is still soap residue in the lines. Use a clarifier or check your pH levels to bring the water back to clarity.
Persistent smells indicate that the biofilm purge was not 100% successful. If the smell remains after shocking, you may need to perform a second purge and drain cycle.
Off-Grid and RV Hot Tub Tips
For those living a more self-sufficient lifestyle, water is a precious resource. You might not want to dump 400 gallons of water if you don’t have to.
However, with a tub that has been sitting, reclaiming the water is rarely safe. The risk of Legionnaires’ disease or skin infections is too high to skip a full drain and refill.
To be more sustainable, use the old water (if not heavily chemically treated) to wash down your driveway or patio. Always check the local regulations regarding “greywater” disposal in your area.
If you use a portable or inflatable tub, the cleaning process is the same, but you must be extra careful with the vinyl. Use only vinyl-safe cleaners and avoid all harsh solvents.
Frequently Asked Questions About Cleaning a Sitting Hot Tub
How long can a hot tub sit empty without damage?
A hot tub can sit empty for several months, but the seals in the pumps may dry out and crack. It is best to leave a small amount of water in the lines or use a “RV antifreeze” if you are winterizing it for a long period.
Can I use bleach to clean the shell?
You can use a very diluted bleach solution (1 part bleach to 10 parts water), but it is harsh on the acrylic and the gaskets. A dedicated spa cleaner or a mixture of white vinegar and water is generally safer and just as effective for surface stains.
What if my hot tub has a “rotten egg” smell?
This smell is usually caused by sulfur-producing bacteria in the plumbing. A deep purge with a professional line cleaner followed by a high-dose chlorine shock is the only way to eliminate this odor and the bacteria causing it.
Do I really need to purge the lines if the water looks clear?
Yes. Biofilm is often clear or hidden deep inside the PVC pipes. Even if the water looks fine, the bacteria living in the pipes will quickly contaminate your fresh water and can cause “hot tub rash” (folliculitis).
How often should I clean a tub that I only use occasionally?
Even with light use, you should drain and refill your hot tub every 3 to 4 months. If the tub is sitting unused but filled, you must still maintain the sanitizer levels weekly to prevent it from becoming a health hazard.
Final Thoughts on Restoring Your Spa
Taking the time to learn how to clean a hot tub that has been sitting ensures that your outdoor sanctuary remains a place of relaxation rather than a source of stress. A systematic approach saves you money on chemicals and prevents long-term damage to your pumps and heater.
Always remember to wear gloves and eye protection when handling concentrated pool chemicals. The process might take a few hours of active work, but the result of soaking in pristine, safe water is worth every bit of effort.
By following these steps, you are not just cleaning a tub; you are maintaining a piece of equipment that supports your outdoor lifestyle and well-being. Stay safe, keep your water balanced, and enjoy your well-earned soak!
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