after washing, the mop pads still smell musty and aren't getting clean.

Diagnosis

The musty odor emanating from your Roborock S8 Pro Ultra mop pads is typically caused by "biofilm" buildup—a colony of bacteria and mold that thrives in the damp, dark environment of the dock. Even though the robot washes the pads, if the agitation isn't sufficient or the water temperature is too low, organic debris (like skin cells, pet dander, and food particles) remains trapped in the microfiber weave. Over time, this creates a sour smell that persists even after a wash cycle. Furthermore, this is often exacerbated by a failure in the dock's drying sequence. If the warm air drying isn't fully penetrating the pads, or if the pads are overlapping during the drying phase, moisture remains trapped in the center of the fabric. You can confirm this by peeling back the pads after a drying cycle; if the center is still damp while the edges are dry, the airflow is insufficient to prevent microbial growth. Additionally, if you are using third-party detergents, they may be leaving a sticky residue that actually attracts more grime and traps odors within the fibers.

How to Fix It

To eliminate the smell and ensure a deep clean, follow these precise steps to optimize the hardware and software settings:

1. Deep Clean the Pads: Remove both mop pads and soak them in a mixture of warm water and a small amount of mild dish soap or white vinegar for 30 minutes. Scrub them manually with a soft brush to remove the biofilm layer that the dock cannot scrub away. Rinse thoroughly and air dry completely before reinstalling.
2. Adjust Wash Intensity: Open the Roborock App. Navigate to Settings > Dock Settings > Mop Wash Settings. Change the 'Wash Mode' from 'Water Saving' to 'Deep'. This increases the volume of water used and the duration of the scrubbing motion, ensuring more debris is flushed into the dirty water tank.
3. Optimize Drying Time: In the same Dock Settings menu, locate 'Mop Drying Time'. If it is set to 2 hours, increase it to 4 hours. This is critical in humid environments to ensure the pads are bone-dry, preventing the "sour" smell from returning.
4. Clean the Dock Base: Remove the mop pads and use a damp cloth to clean the washing tray at the bottom of the dock. If there is a buildup of slime or debris in the tray, the robot is simply washing the pads in dirty water.
5. Flush the System: Fill the clean water tank with a small amount of official Roborock Floor Cleaning Solution (approx. 5ml). Run a "Mop Wash" cycle without the robot attached to clear the internal lines of any residue.

If That Didn't Work

• Replace the Mop Pads: Microfiber has a lifespan. If the pads have been used for more than 3 months of daily cleaning, the fibers may be flattened or clogged with minerals (hard water scale), making them unable to absorb water or release dirt. Replace them with genuine Roborock S8 Pro Ultra replacement pads.
• Inspect the Dirty Water Tank: Check the float sensor and the seal of the dirty water tank. If the tank isn't sealing perfectly, it can create a vacuum leak that reduces the suction power of the mop-washing system, leaving more dirty water on the pads.
• Hard Water Treatment: If you live in an area with hard water, calcium deposits can clog the small spray nozzles in the dock. Fill the clean water tank with a 50/50 mix of distilled water and white vinegar and run a manual wash cycle to descale the system.
• Manual Sun-Drying: Every two weeks, remove the pads and let them dry in direct sunlight for 2-3 hours. The UV rays act as a natural disinfectant that kills the bacteria the warm-air dryer cannot reach.

Heads Up

• Avoid Bleach: Never put bleach or harsh chemicals in the clean water tank; this will degrade the rubber seals and plastic tubing inside the dock, leading to permanent leaks.
• Empty the Tank Promptly: Do not let the dirty water tank sit for more than 48 hours. The stagnant water creates a smell that can actually "back-flow" into the mop pads during the washing process.
• Check Pad Alignment: Ensure the pads are velcroed perfectly flat. If they are bunched up, the scrubbing brushes in the dock won't make full contact, leaving "dead zones" on the pads that smell.
• Use Distilled Water: If you notice white flaky residue on your pads, switch to distilled water to prevent mineral buildup in the dock's internal pumps.