mouldy bathroom tiles

I was daft enough to have my bathroom tiled with fake mosaic tiles. The property is now rented out. Although my tenants are clean, the grout between the tiles and the pretend ground around the fake little mosaic tiles is full of mould.
I have tried normal cleaner and bleach and also stuff from Lakeland specually for mould. But any bright ideas for getting rid of it?

I also need bright ideas for preventing it! If I lived here, I'd ventilate my bathroom more and also wipe down the tiles after every shower (we do that at home!) But tenants won't do that!