Plant tips turning brown.

I have four otherwise healthy plants(went 12/12 on 03/14) that starting going brown on the tips going from top of the plant down to about 1/2 way down with quite a bit of stretch a week ago. One plant shows this in almost all upper fan leaves, the others are much less severe.
My plants might have been too close to the light, I guessed heat and increased the space for the lights. The temps are around 25-26c now, the problem has slowed to slight yellowing behind the brown tips and I think the stretching has also basically stopped, which might have also been the flowering spurt.

Have I diagnosed this correctly, is it heat? Is it normal to keep seeing a slowing browning happen, maybe another 1-2mm, after fixing the light?

Thanks.

wheres the pics

Nute burn? need pics

no pics no tell what you got going there dude.

Oh great swammy, ah yes...you got 'em in store bought dirt and they are under 4-600w/hps. Cut your soil with something like coco, 50/50.