Why do the leaves look like this tight yellowish l...

Hey Growmie, this is one of the classic signs of cannabis magnesium deficiency. You may also see red stems. If you don’t react to it promptly, a cannabis magnesium deficiency can spiral out of control and cause your plant to lose a lot of lower leaves quickly. The plant will pull magnesium out of older leaves and bring them to the newer leaves. That’s why a magnesium deficiency usually appears towards the bottom of the plant and on older, less important leaves. The edges of the leaves may become yellow or bright green and may start feeling crispy to the touch. This crispiness around the edges is different from nutrient burn, which does not lighten the margins inside the leaves. Often with this deficiency, the magnesium is present, but the roots cannot absorb the magnesium properly due to an improper pH. The way you fix this is to flush your plant with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients that includes magnesium. This will remove any nutrient salts that may be affected by the uptake of magnesium and help restore pH to the proper levels. Hopefully, this was helpful and remember ..."Happy Growing" and "Free your mind one puff at a time"