[sidious]

firstly, put the HPS approx 8" from the tops of the plants, as long as the temp is o.k......block up a normal thermometer to the height of the highest plant and keep the temp between 70-80.......when the light is this close the temp will raise, hence why you should have a fan blowing across the tops of the plants.....this distance will help make the plants more bushy.......i keep my lights on 24/0 for veg and then straight to 12/12 when they hit approx 12-18"......however if you want a bigger yield and have room, and also time then grow bigger........just bear in mind that the plant will double or triple in size when fully flowered.........as for the ferts, only after approx 20 days....or before if you like but 1/4 strength....hope this helps......Peace out.....Sid