Shower tray seal?

[John.Stitch]

On the joint between the tray and the first line of tiles there is a line of water on the joint. I wipe this away with a tissue and the water reappears. It seems that the water comes from behind the joint and so the seal is not waterproof?
I used Ban microflex grout and then sealed it with spray on grout sealer.
Behind the tile is tile backer board.
My concern is the black mould growth which developing in about 5 places on this shower tray joint.

 

[tommyl18]

The shower tray should be sealed with silicone to the backer board when it is first fitted and then once you have finished tiling and grouting you then silicone around the silcone tray again so it then has a double seal, it is the same principle with a bath.

 

[foxhole]

And the mold is down to lack of ventilation in the shower area.