you say you are watering them twice a day, is that just little and often then.
when watering plants little and often the water doesnt get to the bottom of the pot and the roots can turn up looking for moisture... you dont want that to happen. its ok to let the top 2 or 3 inches of soil dry out between waterings. usually every 2-3 days.

when a plant needs water, water it well. when it doesnt need it dont water it at all. go to overgrow.com for advice on watering.. its all there.. good luck.