Why my buds are small?

Plants don't read apps and will be ready when they are ready and not due to any sort of theoretical instruction sheet! Seriously though....... A couple of your plants look like they will still need 2-3 weeks of growing to do, so don't stop feeding too early. I have found harvesting when there are about 95% brown pistils as the best time to get buds with peak THC levels. In reality, 150watt LED lights don't really have what it takes to grow super chunky buds. As a recommendation, try some Sweet Seeds seeds, they have awesome genetics with super chunky buds easy to obtain. You can see some pictures of many of their strains in some of my diaries if you are keen. Hope this helps, Organoman.