Leaves of Ti plant getting brown from edges inward. what is causing this?

Betty - most likely to be too much fertilizer,BUT it could be fluoride in the water if you use tapwater, or a watering problem of either too much or too little that each have the effect of damaging to root system and thus causing a shortage of water in the plant.
Sorry, take your choice. Only you know what you have been doing to the plant, and can judge how to correct the problem. Derek