Water the plant from above heavily and let it drain, Watering any plant by soaking it should only be done when a plant has dried to the point of wilting, as it should really be considered as an emergency procedure. Normal watering should always be from above. By watering from above you remove any salts (from fertilizers) that are accumulating in the substrate. Watering by soaking plants does not do this. Add the fact that you are adding fertilizer to the water, this may be your problem.