Hey, why not check the roots? Or, if you're feeling adventurous, why not try repotting? Do you think the roots might be rotting? If they are, it might be because you're watering them too much. If not, there might be another reason. It could also be a sign of pest problems. Do you see any signs of pest rings? If you do find a pest ring, be sure to use anti-pests often when the problem of brown leaves occurs.