It's really hard to know what't happening especially without seeing it, but it sounds like the plant is possibly diseased or distressed. First thing I would do is to cut the dying leaves off very near the base being careful not to cut into other leaves. A leaf 2/3's dead is not going to benefit the plant but might allow disease or rot to spread if left on the plant. Secondly I would look to see if I could tell what's causing the problem. Is the plant allowed to set in water after it's watered? What kind of soil is it planted in? These plants are usually pretty tuff if they are in decent soil and watered correctly.

Some species do have a dry apex. I would check out those roots, and this is the wrong time of year to be watering. I don't care where you live No. of the Equator. Follow the advise above. Norma