over watering is usually caused by watering too often rather than by the amount of water used, if you are using too small amount of water this small amount may be wicking away from the roots since the plant is still small the roots would be too, this would cause the need to water more often risking also over watering, i think its better to water to runoff as suggested above and them let it go dry enough before the next watering, but i cant say if this is being caused by over or under watering for certain.
i grow in coco but my rule to watering is to let it go just a bit dry so the plants show signs it needs water, then i can feel the pot weight and i can get a fell for how periodically i need to water that plant, the next watering would be done a bit earlier than this só the plant don't need to get to this point again, with time you get a feeling from just grabbing the pot and raising it by hand.
