A pic would help but here are some suggestions.
Watering when the top of the soil is dry is not an indication that the rest of the soil is. The leaves will start to droop (from the bottom up) when the plant encounters a lack of water. Or you can try and eyeball by using the weight of the pot - dry vs wet.
The yellowing of the fan leaves can be from lack of nitrogen and you should see it worse near the bottom area of the plant - begins fading at the tips and works backwards - if it is the case then it sounds like it is just beginning. But again the type of yellowing can differ for different deficiencies. If it was a nutrient burn the tips would begin to look crispy and brown (and sometimes curl).
Leaves curling under can be from a lack of phosphorus as oppossed to drooping that an overwatered plant would do.
It is always good to provide as much information as you can. Lights, fertilizer type, soil, pot size, etc....
Go here as well: http://www.mjguide.com/
There is a copy of the Overgrow Plant Abuse Chart see if what you are describing fits.