drooping leaves on top of white rhino plant

hi can any1 help me with my white rhino plant , it is 2 weeks old in veg an the top leaves started curling inwards slightly on the edges an today they started drooping the new leaves coming through are of lighter green then rest an also look slightly crinkly/slightly. , i am using 600w light an it is hung above by bwt 5 foot , could it be that light is to high or too low??? what recomeded hight should i have light hung as it is about 10 inches tall an the 4th set of leaves are coming through. an i have just started feeding them with aqua vega , i am adding 10mil of vega A then 10mil of vegaB, this is at a quarter of recomended dose . also i am thinking i am mayby over feeding them , i feed them every three hours for 15 minutes whilst the light is on its 18 hour cycle so it has six feeds .. is this too much if so how regular should i feed them , i am doing them in hydroponics / stones. any help would be appreciated , oo an i also have fan on constantly is this correct......... other then the drooping the plant looks to be in o.k health stem looks very healthy