How Do I Clean Biofilm From a Spa?

How Do I Clean Biofilm From a Spa?

Biofilm is one of the most common hidden problems in hot tubs, and it often shows up even when the water looks clean. It forms as a slimy layer inside plumbing lines and jets, trapping bacteria, oils, and organic debris. If left untreated, it can cause cloudy water, foam, bad odors, and sanitizer that never seems to hold.

Understanding how biofilm forms and how to remove it properly is key to restoring clean, healthy spa water and preventing the issue from coming back.

What Causes Biofilm in a Hot Tub?

Biofilm develops in warm, low-light environments where water sits inside pipes and plumbing lines. Hot tubs are a perfect match for this.

Common contributors include:

  • Body oils, lotions, cosmetics, and soaps introduced during use

  • Low or inconsistent sanitizer levels

  • Infrequent circulation or long idle periods

  • Dirty or overloaded filters

Even a well-maintained spa can develop biofilm over time because standard sanitizers don’t always penetrate the plumbing walls where it hides.

How to Remove Biofilm Safely and Effectively

The most effective way to remove biofilm is with a spa-specific pipe purge or plumbing cleaner. These products are designed to break down the oily, organic material that sanitizer alone cannot remove.

Start with warm water and remove the filters so the cleaner can reach all internal plumbing. Add the purge product according to the manufacturer’s instructions, then run all jets and pumps for 15 to 30 minutes. During this process, you may see foam, brown residue, or particles rising to the surface. This is normal and indicates the biofilm is being released.

After circulation, drain the spa completely. While the tub is empty, wipe down the shell, jets, and waterline, and rinse or deep-clean the filters. If the filters are heavily coated or worn, replacing them can help prevent the biofilm from returning.

Once refilled, balance the water chemistry and immediately establish proper sanitizer levels to neutralize any remaining bacteria in the system.

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