What is a good watering schedule?

okay I had root gnats and I over watered as of day 21. This plant has been so stressed. I really don't want to stress her out by under watering now. I covered the top 1'4" or so with sand to help with the gnats and it's looking good. I just need to know maybe what the amount per size or just a good way of knowing when to water. I'd like to keep her from turning yellow. Help is much appreciated.

There she is at day 21 of big bud strain.

well all u gotte do is water like every two days its not too bad being under watereed is betetr then over watered