Need help with possible nutrient deficiency...PLEASE HELP!!!

I am using a enn and flow system using fox farm nutrients. I am growing mostly heavy indica strains but i have a few high sativa strains int he same table. yesterday i noticed for the first time, on the sativas mostly, there were brown spots on some of the leaves, and some of the leaves were even almost dead. I am using the fox farm about half strength because people told me fox farm is known for over nuting. I am posting pictures, can anyone give me some advice or tell me what is wrong with my plants? Some more info about the setup is, im using ro water, fox farm 3 part, and 3 part soluable, cal mag, 45 gallon res, 23 plants in 3X8' Table, exhaust, air condition, everything is pretty much done right. I have 2 1000 watt air cooled lights, about 12 inches from plants. Please someone help, i really dont wanna loose this crop. Thanks, and happy growing everyone.

I'm no expert, but almost always the sativas will require less nutes than the indicas. Are the brown areas showing up mostly on the indicas or sativas? From the photos you posted, it actually looks like photo 3 is an indica, and has a deficiency, however photo 4 looks like one of the sativas, and that one looks like nutrient burn. It's tough to grow multiple strains from the same res for that reason, but you already know that. I would just try to keep PH levels consistent, and try to find a happy medium between the different strains. Do you know what your EC is currently?

the ppm is 940. do you think that is too high>?

Your setup sounds pretty good, and the plants shouldn't be having any issues at 940. If anything, I would guess that the indicas would like to be closer to a ppm of 1200 at this point. Those sativas are really going to throw off your grow. Personally, I would just make sure the indicas are happy because you'll get the bigger (and earlier) harvest from those, and then just hope that the sativas can hang on. Do you know your PH level? That can make a big difference also. For rockwool, you'll want to keep the PH level around 6, but also keep in mind that rockwool initially has a very high PH until it has been completely flushed out.

it may be ok for one strain but not another,thats why growing 2 or more strains is difficult.is there any way you could seperate them,I had issues with growing 2 differant strains so I seperated them and all was fine ,I grow in dwc so it wasnt to hard except the roots were very tangled togeather.as for the spots on those leaves have you sprayed them with anything,I have a hard time going by pics.it may be nute burn but at 940 I doubt it,are you going by .7 scale? I keep mine around 1000 ppm and havent had any burn on my sativas,however I took some advice from someone on my first grow and was running at 1400 lucas formula and got a bad burn now I stay under 1100 and havent had any burn. good luck

I am mostly having the problems with the sativas. The sativas are from a buddy's plants and the indicas are from seed. Only one leaf that i have noticed on the indica is affected. I have not sprayed the leaves with anything except water, and i haven't done that much. I don't know what you mean by .7 scale, but i have a nutradip trimeter and it says 940. I keep the ph from 5.8-6.3, my setup raises from 5.9-6.2 in a day, i usually add around 1 oz of homemade ph down (Sulfuric acid and RO water), and that brings it back to 5.8-5.9. Should i check the pH twice a day instead of once a day? One thing i am not sure of is when i use fox farm, i change my res every two weeks. On fox farms schedule, http://foxfarmfertilizer.com/hydrofeed.pdf it says i have to add 3 tsp per gal of grow big on week 3, and on week 4 it says 3 tsp. My question is, do i add 3 more teaspoons on week 4, or since i change the res every two weeks, the first week grow big is enough? It confuses me because if i had to add 3 teaspoons in same res seems like my ppm would be way too high? But, in the week four i add big bloom 1 tbl spoon per gallon and open sesame, but by this time, the grow big has been in my res for a week, and we've been topping it off with RO water, so wouldn't b y the 4th week schedule, the grow big be real weak, and need more? Also, am i supposed to add fert when i top of my res? it drops about 5 gallons every 2 days. Thank you so much for your help everyone, your really getting my trust built up with forums (Ive never really asked questions before, i didn't think people respond) Thank you and happy growing. ALSO, I dont know if i can remove them, they are in 4 inch rockwool on top of rockwool slab, can i?

Sativas are more difficult to grow. For your purposes here, you'll never need to spray the leave with anything. What cgrizzle meant by .7 is the conversion factor used to calculate ppm. Different companies use different conversion factors to determine ppm. Just as we use torque to calculate horsepower in a car engine, we use the EC to calculate the ppm in our res. All you need to do is divide your ppm by the EC. For example, if my my ppm reads 1000, and my EC reads 1.42, then I will divide 1000 into 1420 and get .70, and this is a ".7" conversion factor. So if your ppm reads 710 and your EC is 1.42, then your conversion will only be .5 and that makes a big difference. This is why everyone should really just go by EC and then there wouldn't be any confusion.
As for your res, you should be draining your entire res about once a week. Then refill with low ppm water, add your nutes for that stage of growth, and then adjust the ph to around 6. Otherwise you end of with a wacky mix of nutes, and who knows what'll happen.
Hope that helps.

Im posting more pictures of what my problems are, maybe someone can better diagnose them. Thank you for your help everyone...