The number one killer of indoor house plants is over watering. Check the soil you have them planted in and make sure it drains quickly, don't be afraid to let it dry out in between watering. Be consistant, if you water once a week, water on the same day. The other things to check are sufficient lighting (but not by a window where the sun can come through the glass and burn the leaves) and humidity (add a tray underneath with pebbles and water). From what you describe, your problem is not lack of fertilizer, but when you do fertilize, use a liquid. Fert sticks are too centralized. Sorry to say, you may go through a few plants till you find the correct place/conditions in your home.