That my friend looks like nutrient burn, which is pretty common if the plant's been overfed. Overfeeding, especially with too much nitrogen, can cause brown spots, crispy edges, or darkening of the leaves. It’s also possible if you’re in the process of flushing, as the plant may not be getting enough nutrients, which can cause deficiencies and result in similar brown spots.

If you’re overfeeding, try reducing the nutrient strength and cut back on nitrogen while focusing on higher phosphorus and potassium, which are important for the late flowering phase. If you're flushing, make sure you're not doing it too early or too abruptly, as that can stress the plant and lead to nutrient deficiencies.

Hope that helps!