Your shower is the favourite place in the home for bacteria.
Firstly, there’s lots of them, as they are washed off your skin when you shower, and secondly, it’s the perfect environment for them – warm and moist.
Bacteria thrive at room temperature – that’s why we put food in the fridge – it slows their activity dramatically. Freezing them of course suspends it, and boiling kills them (mostly).
And the bacterial activity generates biomass, which appears as black mould. To get rid of it, you want to both kill the bacteria, and destroy the mould.
Luckily, bleach does both, as it is an extremely strong oxidiser, and just blasts the bacteria and mould to bits.
But don’t scrub – just spray it on and let the chemical do its job while you do something else – and make sure the area is well ventilated so the fumes don’t asphyxiate you (they’re not toxic but very irritating).
Next step is BAM Easy Off trigger on the glass – it will rip through the soap scum like a knife through butter.
If the soap scum has been there a while it may have etched the glass, so spray it with Mr Sheen, as the wax film will fill in imperfections and leave a nice wax coating on the glass that will inhibit further soap scum build up.
And clean the floor of the shower afterwards with the BAM- Mr Sheen is slippery, and any overspray that finished up on the floor may be a hazard when wet.