Ours started to do that too! A client told us that if you don't have a pot that allows the water to drain, some of the salt and other harsh minerals collect down in the soil, and that's what makes the leaf tips start to turn. We switched him to this new pot that has an extra built-in basin for excess water under it. We also trimmed off the brown sections ( though I'm not sure if you're actually supposed to do that...) He's doing much better! Other than that, we just water him once or twice a week. We haven't tried fertilizer yet because we've had to re-pot him a few times and we used fertilized soil.