Looking for Help!!

New to site, looking for some advice on what the $#% I am doing wrong ? I have anice clone area under 2x4 flouresnt using e-z cloner with above 90% success except for my purple haze, they seem to need more but usually come back strong after little time in a 50/50 mix of a Happy Frog soiless and a Sunshine #4 . The veg is under a 400 transplanted in 5gl buckets for 2 more weeks usually ending up 2 1/2 to 3 ft tall. Then they slide into a 16x18 red room (light proof) for a full 8 wk cycle. I currently have 2 strains that I like but can't seem to pull it off. Purple Haze and Sour Diesel. I have had this set up for about a year, several grows, seems like it is always something wrong. In Veg it is usually pretty good but the leafs seem to twist from time to time and a slight unnatural curl to them. ( PH? too low in soil?) Back to the red room, powered by 4 1000 watt, each pair being exhausted out of the room by a 8" in-line to the outdoors. I have 2 standard wall mount fans pushing air on opposite sides of the room. I also put a 6" pushing fresh air into room. Seems good to me. So my plants get split into 4 groups spaced out in room and all is usually good through first 4 wks. I start to see necrosis along with drooping branches, curling leaves and set in slowly thru the next 4 wks. My last crop of purple looked great til the end when for the first time actually turned a wierd purple on the leaves and more of niro defiency at the very end. The final product tasted like shit! I used Final Flush. I use General Hydroponics feeding schedule and have tried any where from full dose down to 25% with my liking to be 50%. The variation never seemed to effect my problems.? So i just flushed a group of plants at 4wks bloom with a R.O. water at 7.4 ph and it came out at 6.2! That can't be good??? PH is something I have not followed in the past other than the water i put in, which i usually balanced to 6.3 to 6.7 going in. Does it lower in the soil? On top of the varying problems like necrosis and awful taste I have a Powrey Mildew that is freaking tough! I have been at battle since day 1. I have been spraying foilage twice a week for months with evrything made. Neem oil, Az Max, PM Wash, Serenade and also a milk- bicarbonate mix. Nothing seems to be real effective. What can a guy do? This should'nt be that hard but I can't seem to get it right?

Nothing? No help at all? No experienced growers with ideas?

what is the humidity in that room?

Powdery Mildew is usually strain dependant. I would get a new strain to play with that grows well in your room.

Low humidity and i have seen strain differences but my purple haze never had a problem til this grow. Its winter out and i would have guessed it to be the best indoor time?

try not foliar spraying (except seedlings/cuttings) on a test batch or single plant and post results.