Many automatic pool cleaners not only suck debris off the floor of the pool, but scrub as well. Some can scrub the walls and steps. This is an excellent benefit, especially when your pool is in the shade for some parts of the day. Mould is usually found in the shaded parts before those sunny areas. It is always wise to inspect places such as behind the hand rails and other hardware in the pool which can cast shade onto the pool walls and floor.
However, simply running your hand over the walls below the water line will tell you if mould is starting to propagate before you can see it. The surface of the walls will feel slippery to the touch. It’s essential to get those walls scrubbed down, then shock the pool by adding more chlorine well before you see any black stains.
It’s important to also clean the filters and treat them for mould at the same time, otherwise the spores will remain in them and re-infect the pool after it has been cleaned. It takes some time to clean mould from the pool and it should not be used during this time. To ensure your family doesn’t use the pool, cordon it off with tape and put signs along it.