Green coating on Coco

a little algae - As it gets shielded from light it will die. It is of no risk. It is a reason to reassess watering habits as well as size of pot to plant used. Algae can happen early on with best efforts because seedlngs don't drink fast enough, initially, but if you don't allow the top layer to dry between irrigations, you could be exacerbating it, for example. A tiny plant in a large pot is more likely to get algea, too. even though it is of no concern, i just knock it off at transplant.