Dark Column: Probably column changes are not too remarkable this time, they could be group as a colour darkening. It could be due to an increase bacteria concentration. Top layer is unchanged.
Here, we include an explanation of why dark colour is produced:
Dark area growth indicates the presence of two types of bacteria. Desulfovibrio and Clostridium.
Light column: Water has become orange, mollusk died and bateria dominate the column. In the light zone many bacteria have grown while in the dark zone there is nothing. We can see all around the bottle a very intense orange due to iron oxide. In the bottom we see again the sulfate-bacteria that produce the dark colour and we can also see violet spots that tell us there are sulfure-bacteria.