Biofilm is a bacteria film that can grow in a spa, skimmer basket, or even a filter. This bacteria likes areas that are warm and damp. Biofilms can become resistant to chlorine and bromine. Your spa water quality will decline, you may notice your water starts to turn cloudy and will be foaming, it may also have a very strong odor to it.
Wiping off the surfaces of your spa will lift the biofilm off of the surface to where the sanitizers can get to the bottom layer of the bacteria to kill it. Also make sure that you clean your spa cover, so you don't reinfect your spa. However you will need to chemically treat your plumbing and filters with a product that is made especially for the removal of biofilms. It will also help remove the biofilm scaling on your heater.
By removing any biofilm in your hot tub or spa you should enjoy a longer expectancy to the life of your spa and its filters and heater. Spa owners also will notice it is easier to maintain the balance of chemicals in their spa.