# Slimy inflatable hot tub walls: dealing with biofilm Source: https://bubbleandsoak.co.uk/blog/slimy-inflatable-hot-tub Published: 2026-10-12 Publisher: Bubble and Soak **In short:** A slimy feel on the liner usually means biofilm, a thin layer of bacteria and organic matter that sticks to surfaces and shelters from sanitiser. It hides in pipes, the pump, seams and under the waterline. Clear it with a line purge product before draining, then scrub the liner, rinse well, fit a new filter and refill with balanced water. If the walls or floor of your inflatable tub feel slippery even when the water looks clear, you are probably feeling biofilm. It forms on almost any wet surface, and once established it protects itself from normal sanitiser levels. It often reappears quickly after a refill because it was never removed from the pipes and pump. This guide explains what biofilm is, where it hides in an inflatable tub and a step by step routine to remove it, with habits that keep it away. ## What biofilm is Biofilm is a thin, slippery layer made up of bacteria and the substances they produce, mixed with organic matter from bathers, leaves and dust. It sticks to surfaces in contact with water, particularly where flow is low and sanitiser has dipped. The outer layer protects the bacteria inside, so normal sanitiser levels struggle to reach them. In hot tubs, biofilm can cause cloudy water, smells, foam and sanitiser that disappears faster than expected. It is a sign that the water care routine needs a reset. ## Where it hides in an inflatable tub Because much of it is out of sight, scrubbing the liner alone is rarely enough. The pipes need a purge with the pump running. - Inside the hoses between the tub and the pump unit. - Inside the pump and heater housing. - Around the inlet and outlet fittings and the filter housing. - Along the liner seams and the floor edge. - At the waterline, where oils collect. - On the underside of the cover. - In the AirJet channels if water gets into them. ## Purge, scrub and refill Do not use household cleaners, bleach sprays or abrasive pads on the liner unless the manual allows them. They can damage the material or leave residues that foam. See [how to drain an inflatable hot tub](https://bubbleandsoak.co.uk/blog/how-to-drain-inflatable-hot-tub) for draining methods. 1. With the old water still in, add a hot tub line cleaner or purge product as the label directs. 2. Run the filter pump, and the jets if the label says so, for the time stated so it circulates through the pipes. 3. Switch off and unplug the pump, then drain the tub. 4. Remove the filter and set it aside to clean or replace. 5. Wipe or gently scrub the liner, seams, waterline and fittings with a cleaner suitable for hot tubs, using a soft cloth or sponge. 6. Clean the underside of the cover. 7. Rinse everything thoroughly so no cleaner is left behind, and drain the rinse water. 8. Fit a clean or new filter, refill and balance the water before heating. Note: Wear gloves when handling purge products and cleaners, follow the chemical maker's instructions and keep everything out of reach of children. Unplug the pump before draining or cleaning around it. ## Why it keeps coming back Biofilm returns when sanitiser drops low for a while, when the filter is dirty or when water sits still. Tubs left full but switched off for days, or with the filter pump running only briefly, are at higher risk. Leaves and debris getting under the cover add food for it. Hot tubs are also a known place for bacteria to grow if water care slips. The HSE publishes guidance on managing spa pool water; for home owners, the simple message is to keep sanitiser in range, filter regularly and drain and clean often. ## Keeping it away A regular purge before every drain and refill is the single best habit against biofilm. See [what chemicals a hot tub needs](https://bubbleandsoak.co.uk/blog/what-chemicals-does-a-hot-tub-need) for a weekly routine. - Keep sanitiser in range and test a few times a week. - Run the filter pump for the hours the manual recommends. - Shock weekly or after heavy use. - Rinse the filter every few days and replace it when worn. - Purge the lines before each drain. - Keep the cover clean and on between uses. [See our hot tub shortlist](https://bubbleandsoak.co.uk/best/best-inflatable-hot-tubs) ## Cleaning the cover and filter The underside of the cover sits in warm, damp air and collects the same film as the liner. Wipe it with a cleaner made for hot tub covers, rinse and let it dry before refitting. An inflatable cover can be turned over and aired on a dry day. Filters trap much of the organic matter that feeds biofilm, so a filter that has been in the tub through a slimy spell is best replaced rather than rinsed. Keep a spare so you can swap it straight away, and clean the old one with a filter cleaner before storing it. See [how to clean hot tub filters](https://bubbleandsoak.co.uk/blog/how-to-clean-hot-tub-filters). ## Frequently asked questions **Why is my inflatable hot tub slimy?** Usually biofilm, which builds up when sanitiser dips or the filter is dirty. **Will shock remove biofilm?** Shock helps, but biofilm in the pipes usually needs a purge product before draining. **Can I use bleach to clean the liner?** Use cleaners made for hot tubs and follow your manual. Household products can damage the liner or cause foam. **How often should I purge the lines?** Before each drain and refill is a good habit, following the product label. ## Buying guides on this topic - https://bubbleandsoak.co.uk/best/best-inflatable-hot-tubs - https://bubbleandsoak.co.uk/best/lay-z-spa-models-compared ## Sources - [HSE: Legionnaires' disease](https://www.hse.gov.uk/legionnaires/)