Begginings of Nute burn or Overwatering?

Hi, im growing Afwreck indoors, 400w MH veggin for 20 hours on, 4 off, in Hydroton,

watering 4 times a day pump on for 3 min (drains out in less than a minute).

Recently increased nute solution to 2/3 recommended mature vegetative (20ml/gal Pure Blend Pro grow 3-2-4)

I bought established clones (about 2 weeks old), have vegged for 2 weeks more (4 weeks total), some showing tips of roots coming out of bottoms of pots.

One of the plants shows no problems, some only show issues at the top (I raised the light a little but no change), and some only at the bottom leaves...

It is a little warm (27*C), and i bought a new fan but it hasnt arrived yet...

Heres some pics
only plant showing problems at the top and bottom:


Second plant, showing discoloration inside leaves:




thanks for any help!

wont let me post images so I'll link them
Third plant showing problems at top:
http://img96.imageshack.us/i/20100707000618.jpg/

and this plant showing some problems on the bottom:
http://img84.imageshack.us/i/20100707000639.jpg/

and this plant is the biggest, has most new growth, and looks mostly healthy, maybe a few slightly browned tips:
http://img85.imageshack.us/i/20100707000624.jpg/

Fan arrived today, but temps are down to 26*C, did get some algae growth though, could that be causing this?

does anyone know what I could do to correct this?

I changed out the resavoir and am going to flush for a few days and see what happens, does that sound like a good route to try to fix this? How often should I water?

would silica additive help out? should strengthen the plants and help out with the heat

still no improvement, also tested pH again with new paper, and its fine

nute burn probable

yea, thats what I figured, Im flushing right now and only watering twice a day, well see what happens

Call me stupid but it looks more like a lack of mag. with a little burn. So to much on the npk not enough mag.

im using unfiltered tap water, figured it wouldnt be a problem, should i be adding cal mag?

I use unfiltered water and seem to have to add mag to my nutes.

guess ill go get some, we have relatively hard water so i figured it wouldnt be necessary, guess well find out, thanks

plants looking healthier, can I expect the brown tips to ever go away though?

nope it there as long as the leaf is.