Brown spots on leaves and drying up on the ends

Ok ...please help me ....i have a stealth hydro bubbleponic setup....i have the (2) 85watt(1red/1blue) cfls that came with it plus i have added another 105 watt of blue spectrum cfl...im using half the recomended nutient packs to the 6 gallon resevoir (that i filled with distilled water) because my plants are only 3 weeks old....the temp is 78 degrees ...and the humidity is 45% i have them in a 4x4x4 growbox with a oscilating fan blowing on them and (2) 105 cfm fans blowing air out the top and (2) passive air intakes at the bottom that are 4"x9" . Im using white widow seeds from holland and the ph of the water is 6.0 and the water temp is 75 degrees....what am i doing wrong ...i did let the water level drop for a couple of days...it went down about a gallon or 2 ...down to about 4-4.5 gallons from 6 gallons...but i changed out the first half strenght solution and replaced it with fresh water and the other half packets of the nutes....but im still seeing these brown and yellow dry sopt that become brittle... ...its getting light 24/0 and at first i had the lights within an inch or 2 ...but when i started to see the first spots i raised them to about 10 inches....could the closeness for that fisrt week have caused this problem ...?

 

IT LOOKS LIKE its the nutes...its very cool in the box....the plants look sick ...when i changed the nutes i gave them like 24 hrs or more of just plain water b4 i put the half strength nutes in there...im about to go check them again...

 

Im using 1/2 pack of the micro and 1/2 pack of the grow...im trying to keep my ph at 5.8.....and where should my ppm be....??? i also have 3 different sized plants in the unit due to late sprouting and other issues...but i started the half nutes when they were 2 inches tall ...but they only have 4 leaves on them ...is this still too soon for nutes ...??