all the bottom leaves are showing through but now the last few days some of the fan leaves have like pale burns and the very bottom ones have shriveled and gone crispy with brown bits(not really starting fom edges though,the rest of the leaves look fine,my ppm is 850 and my ph is 5.6/5.9 so would that be nutrient burn,im using a 400w multi spectrum lamp/bulb 18/6 about 17/18" away from top of plants in a hydro ebb n flo,using rockwool,temp is 27 degrees, flooding 15 mins every 6 hrs in the light(3 times a day)and there are 6 three week old white widow,dark i dont flood,i know i havnt got pests but does everything sound right and look right or am i doing anything wrong? hope u can help me.
here r a few pics,u can see what i mean on the close up shots.

thanks people
sc0usa Reviewed by sc0usa on . help(pic) all the bottom leaves are showing through but now the last few days some of the fan leaves have like pale burns and the very bottom ones have shriveled and gone crispy with brown bits(not really starting fom edges though,the rest of the leaves look fine,my ppm is 850 and my ph is 5.6/5.9 so would that be nutrient burn,im using a 400w multi spectrum lamp/bulb 18/6 about 17/18" away from top of plants in a hydro ebb n flo,using rockwool,temp is 27 degrees, flooding 15 mins every 6 hrs in the Rating: 5