Since you aren't using any nutes and trying to use a living soil, chances are that you are having a touch of low nutes. Living soil is great if you can pull it off, but I feel that it is much harder to keep the soil growing and living than growig a plant in it. I think living soil works best outdoors but indoors it is a difficult task. All of the ingredients might be in there but unless the flora in it is thriving, nothing gets broken down into a form the plants can use. If you are well into flowering, there isn't much you can do at this point. Plants will naturally start to draw stored nutrients from the larger fan leaves... many times the plant will lose most if not all of them, leaving just buds.
I don't know how to test if your soil is still "living", but it looks to be a little low on nutes... something to keep in mind for the next grow.