Good morning, I have a question and I hope someone can help me. I have as inoculum chlorella vulgaris, with photoperiod of 12/12 hours, shaker agitation up to a volume of 500 mL and agitation provided by fish tank pump for volumes of 1 L and up. In my culture I have observed two phenomena:

In the attached images you can see the separated biomass that tends to accumulate at the bottom as if it were separated into two phases, likewise it remains as suspended particles in my medium, although even so in a certain time this tends to darken although it is not completely homogenized. I have also observed the formation of a foam on the top of my crops, which I associate to a bacteria producing it but I have not been able to control that, any recommendations?

Also in the upper part of my containers it is forming like a green slime where my microalgae are staying and although I try to homogenize them they do not unite. Could this be associated with