Puzzling problem help me out? Lsd and pineapple strains

Hey all i need some help, i've done plenty of reading around and have lots of info but i can't nail down just what it might be. I have three lsd, two pineapple chunk and two pineapple express auto's all 4 weeks from seed, things were a bit slow to start but they blew up between week 2 and now but i've noticed a small problem appear in the last few days, the smallest and newest leaves appear burnt on the tips, this is fairly consistent over all the plants top to bottom and a couple of the older leaves have crispy brown edges but all the stems are vibrant green and growth still seems fantastic, they are being fed dutch master gold a+b, zone, add.27, silica and have been foliar fed once with liquid light and saturator. Ppms are around 850 and ph is always at 5.5, temps stay between 72-82. Only thing i could think that has changed was the liquid light and saturator and i also added another small dam to blow the breeze on the babies. From what i've read it could be a potassium def, wondering if it could have been the foliar spray or wind burn? If it helps i have noticed the two largest, one lsd one pineapple chunk seemed to stretch out the node spacing by almost double after the 5th or 6th sets although i have heard these sativa dom hybrids from barneys start off looking more indica and then switch. Any help would be greatly appreciated i'll put some pix up asap

PPM at 850 sounds pretty high for that stage suggesting nute burn. Especially only 4weeks from seed. My PPM is usually between 800-1200 when I'm close to and during flowering. I advise to back of the nutes a little. But I'm sure a guru could tell you exactly what possible definciency is going on, but it sounds like nute burn to me.

I thought it may have been burn but the problem only seemed to occur when i backed off my nutrient strength to 800? Before the tiny tip burn problem they were going great guns, they are still now. The budsites on the auto's seem a bit lacklustre too, pistills aren't extended etc, this could just be that they need switching to flowering nutes but everything i've read seems to signal a potassium deficiency especially with the slight stretch since the problem appeared

Two quick notes if it helps you guys help me, flushed thismorning with very weak nute solution but the problem only seems to be progressing and the ppm of 850 is including my base tap of 330ppm so i'm really only adding about 500ppm in nutes