tips turning light color but only about 1/4 in long..Potassium? Pic.

Please look at these photo's .Just the very tips on 60% of the palnt and they are only about 1/4 inch each and not getting bigger. I'm in dwc 5 gal buckets using GH nutes w/calmag and b52. Plants are 6 weeks and other than that are very healthy. Just trimmed some fan leaves, could that have any thing to do with it. Ph is good by chart reading not meter, and ppm is 750.Not heat issue,.. I use LED'S w/ fan room temp is 75 and Rh is 65.I vent by leaving my closet door open.Again it's not browning it's more of a light color and not more than 1/4 inch and just on the very tips, but it's the same look on all that are an issue.I don't believe its a cal or mag issue. Anyone seen this before?
It'IMG_20121212_132144.jpgIMG_20121212_132251.jpgs hard to see on first pic, dead center on second pic Under led's it's brown and under white light it'sa light color
 
Top