In my opinion, you can overwater coco.. however, if you are hand watering it becomes harder to do. yes coco has a threshold for water intake which cannot be exceeded, but if you do not let the pots dry out the roots will not stretch to their maximum looking for food since the soil is constantly saturated. Now the amount of times you water a week depends on the size of your container and stage of growth. I water 3 gals every other day or every three days depending on height of plant, with 5 gals i go every four day to third when they start putting the weight on. I have gone longer a day or two just because i had to with little ill effects. For gnats i use diatamacious earth and yellow sticky pads. its the larvae you need to worry about not the adults too much.