what gives you the impression its root rot friend? can you take a pictures of the soil in a better lighting (without the HPS on and maybe a blue or flourescent/natural light will even work better for seeing...is the soil wet or muddy? if so is it wet and muddy all the time? do you have holes drilledi n your pots? how often do you water? when you do water how much water do you give them and how big is the pots...3gallon pots? 5gallon pots? its sort of hard to help without more speicfic facts and details. like one dude siad, it does look more like nutrient burn or at least nutrient burn is present, whether or not thats the only problem...i dont know, its hard to tell....after looking closely at the picture you provided...in the backround there i can see one or two smaller leaves that are curled up quite badly/ look crispy which def. looks like or has signs of some type ofa nutrient burn however, the one big leaf in the pic you shown doesnt look like actual nutrient burn, if you notice the tips of the leaves are yellowing starting from the outside working their way into the leaf...usually nutienet burn starts within the leaf veins in the middleo f the leaf although it can start from the outside in like that, but if it was nutrient burn only the leaves would turn brown, crispy and really curl up like the smaller ones in the back of your pic...honestly it looks like either some type of lockout or maybe even a small deifiency of one nutrient while to much of another nutrient which is causing the burned leaf tips....then on top of that the droopiness looks like some type of overwatering oor somethjing along the lines of that sort but....it could becaused by many different things, both lockout and nutrient burn can cause drooping in some cases but as i said, with only one picture with bad lighting because of the HPS its sort of hard to tell...can you provide more details? this type of thing (drooping like that) can be caused even by it being to hot in the grow room.....so unfortunatley there are many reasons this stuff can be happening...maybe if you could provide some more details and specifics we could help better....stuff to include that can would be: in no particular order of importance...
grow room temperature on average, including high temp and low temp as well as the average
condition of soil on a daily basis (wet, muddy, dry, very dry)
what kind or type of soil (did it have nutrients in it? did you add your own? did you add more plus it had some?, more info the better)
the ph of the soil and water run off if you know it, if not not a huge deal, but it can help big time
how much your feeding daily (feeding schedule, the entire schedule)
how often you water and how much when you do water (includin how many feedings vs just plain waterings)
type of environment?....good airflow? do you have a fan? whats the temp? whats the RH? (relative humidity)
do you know the PPM of your water? (parts per million) can be found out with a PPM meter or an EC meter
whats the PPM before you add nutients, after you add?
not all of this stuff may be necessary to figure out your problem but the more info that you have the better and more accurate answers people can give you. no matter ehat plaese remember that its very hard fofr someone a 1000 miles away form you to just look at your plants in a pic and tell you exactly what wrong or going on...and while some are better than others, thje members of our community can usually help more often than not so, please try to be as specific as possible, the more specific you are the more specific we can be when providing you with answers...either way, good luck friend. peace