Unfortunately this week I found out that one of the main colas had a grey mold. I've since removed the affected buds from the plant as well as a lot of yellow dying leaves. My guess for the mold would be lower temperatures (from a few weeks ago) combined with a raised humidity (after feeding). I've ordered a humidity controlling socket and a dehumidifier and I am going to use this equipment for all of my future grows.
Apart from bad news, I've found out an interesting fact too. The stems of the trichomes are purple here and there :)