You keep your hot tub water balanced, your filters are clean, and the water looks sparkling. So why do you still get persistent foam, a musty odour, or even mysterious black flakes floating in your spa? The answer lies in a hidden problem that plagues nearly every hot tub owner: biofilm.
Biofilm is a slimy, sticky buildup of bacteria, fungi, and other microorganisms that forms on the inside of your hot tub’s plumbing lines and jets. While your sanitizer works hard to keep the water clean, it can’t penetrate this protective layer. Over time, this microscopic colony grows and multiplies, leading to a host of frustrating problems that even the strongest chemicals can’t fix.
This comprehensive guide will show you the best way to clean and remove biofilm and mold from your hot tub’s internal pipes. We’ll cover the tell-tale signs, the essential purging process, and the best products to use for a truly deep clean.
The Unseen Problem: What is Biofilm?
Think of biofilm as a microscopic neighborhood of bacteria. It starts with a few microorganisms clinging to the plastic surfaces of your spa’s pipes and jets. They secrete a protective, slimy matrix that allows them to multiply and shield themselves from your sanitizer (chlorine, bromine, etc.).
This biofilm is the root cause of many common hot tub problems:
- Black Flakes in the Water: As the biofilm matures, pieces can break off and get pushed into the spa by the jets. These can appear as small, dark, oily flecks.
- Persistent Odors: A musty, earthy, or foul smell that lingers even after shocking the water. The smell is a result of the bacteria and fungi living in the biofilm.
- Difficulty Maintaining Water Clarity: The biofilm constantly sloughs off microscopic particles, making it impossible for your sanitizer and filter to keep the water clear.
- Persistent Foaming: Biofilm contains organic waste that can contribute to foaming, even after draining and refilling.
Simply shocking your spa or adding more sanitizer will not get rid of this problem. In fact, it often makes it worse, as the sanitizer struggles against the protected bacteria, leading to more chloramines and a stronger odor. To truly fix the problem, you need to perform a complete hot tub plumbing purge.
When is the Right Time for a Hot Tub Purge?
The best time to purge your hot tub is at every drain and refill, which is typically every 3 to 4 months. This makes it a standard part of your hot tub maintenance routine.
You should also perform an immediate purge if you notice any of the following signs:
- You see black flakes coming from the jets.
- Your water has a persistent, unpleasant odor.
- You are having a difficult time maintaining water clarity, even with balanced chemistry.
- You have just bought a used hot tub and want to ensure it is thoroughly cleaned.
The Best Way to Clean Your Hot Tub Pipes: A Step-by-Step Guide
The process of a spa pipe cleaning is designed to use the spa’s own pump and jets to circulate a powerful cleaning agent through every inch of the plumbing.
Step 1: Choose and Add Your Purge Product
Do not use household products like bleach, vinegar, or dish soap. These can damage your seals, o-rings, and other internal components. Instead, use a commercial-grade hot tub plumbing cleaner specifically formulated for this purpose.3 These products are designed to be non-foaming, pH-neutral, and effective at breaking down biofilm without harming your spa’s equipment.
Add the recommended amount of the purge product directly to the existing, dirty water. Do this a day or two before you plan to drain the spa.
Step 2: Run the Jets
Turn on all the jets and run them on their highest setting. Keep them running for at least 30-60 minutes. The high-speed water flow will push the cleaning agent through every section of the plumbing, dislodging the biofilm from the pipe walls and jets. You may be surprised—and a little disgusted—by the amount of slimy gunk and flakes that appear in the water. This is a good sign that the product is working!
Step 3: Drain the Water
Once the purge is complete, turn off all power to the spa at the breaker. Open the main drain valve or use a submersible pump to completely empty all the water from the hot tub.
Step 4: Clean the Shell and Jets
With the spa drained, you’ll likely see a slimy residue clinging to the shell, especially around the waterline and jets. Use a spa-safe surface cleaner and a soft cloth to wipe down the entire interior shell, paying special attention to the jets and the filter housing. For the jets, a small brush can help scrub any remaining visible buildup.
Step 5: Refill with Fresh Water & Sanitize
With the plumbing purged and the shell sparkling, it’s time to refill your spa. Always place the end of your hose into the filter housing while refilling. This helps the water fill from the bottom up, pushing out any trapped air and helping you avoid a plumbing air lock in your pump. Once full, turn the power back on, heat the water, and then add your chemicals to balance the pH, alkalinity, and sanitizer levels for a fresh, clean start.
The Best Products for Hot Tub Pipe Cleaning
For a truly effective and safe purge, always use a reputable, professional-grade product. These are often sold under the name “pipe cleaner,” “flush,” or “purger.” Some of the most highly-rated brands include:
- O-A-C Hot Tub System Flush: Known for its powerful enzyme-based formula that breaks down biofilm effectively.
- Ahh-Some Hot Tub & Jetted Tub Bio-Cleaner: A concentrated gel that is famous for its ability to produce visible results and scrub away stubborn buildup.
- SeaKlear Spa System Flush: A popular choice that works by oxidizing and breaking down organic deposits in the plumbing.
These products are the secret weapon for any serious spa pipe cleaning regimen.
Ongoing Prevention: The Key to a Clean Spa
While a periodic purge is essential, the best way to avoid a severe biofilm problem is through consistent prevention.
- Rinse Off Before Use: The easiest way to reduce biofilm buildup is to shower before entering the hot tub. This washes away body oils, lotions, and soaps that bacteria feed on.
- Maintain Proper Water Chemistry: Consistently balancing your pH and sanitizer levels is the best defense against biofilm. A well-sanitized hot tub is a hostile environment for bacteria.
- Clean Your Filters Regularly: Your filter is the first line of defense. Rinsing your filters weekly and deep-cleaning them with a chemical filter cleaner every month prevents them from becoming a breeding ground for bacteria.
By making a hot tub plumbing purge a regular part of your routine and adopting these simple prevention habits, you can say goodbye to mysterious flakes, unpleasant odors, and cloudy water. Your hot tub will be cleaner, healthier, and more enjoyable for everyone who uses it.