leafs starting to curl and go brown at tips

[stevo]

plants 3 weeks old using a 250 watt son pt light not sure how far away the light should be. also when do i start adding plant food to it?

[sawleaf]

I'm not sure what type of light you are talking about. Son pt light? You should be feeding your plant already

[del...]

i usually wait until the 3rd-4th week before adding ferts when using fresh, high quality potting soil and then only at half strength and no more than once every couple of weeks...or when they 'ask' for it. a very common cause for leaf curl and dead/dying tips is over-watering...always check the soil before watering. too much can be just as bad as too little (and symptoms are very similar).
a good guide for light distance is place the back of your hand under it and where it begins to feel uncomfortably warm is the very closest it should be...best to add 6-8" to it. watch them closely until you get the feel of your equipment.

the more time/experience with your plants the better handle you'll have on it so go easy with whatever you're advised and common sense is a must. you'll probably read of some odd and extreme 'tricks' (like cutting off fan leaves during veg) here and at other sites but use your head or ask before doing anything permanent.