yellow with nicrosis brown spots..plz help

in fox farm osean forest, first was straight water next was grow big and big bloom lamps were not to close it almost happened overnight, the ends turned yellow folled by brown using well water ph around 6.5 flushed recently dont know if i should get back into npk yetor keep them on plain water, also been keeping 1500 ppms on co2

Could be a magnesium deficiency. Anyone else have any thoughts?

I'm almost positive Mg is the culprit here. The way a lot of the leaves are making a 'V' shape like their trying to close up. And how the yellowing starts at the tips of the older leaves.

looks like mag def

did it start with spots ?
is it spreading ?
if so up or down
i had a mag diff problem
that did look like that
but it started by spotting on the lower
leaves and spread up the plant

It started with yellowing, between the veins then started turning brown before it was all the way yellow it seems like it starts up top and heads down, should i put the girls back on feeding regement? If so full strength? And by the way thanks for the help...

I just looked at the 'plant problem guide' ( http://www.icmag.com/ic/showthread.php?t=11688 ) and it looks and sounds like a mag deficiency, as you suspected. It even mentions the problems sometimes starting in the middle/top of the plant, so it fits pretty well. Read it and see what you think.

Anyone know of a insane asylum....i need to change to 12/12,,,,i feel like the rain man, accept instead of numbers, its cannabis symptoms, speaking of rain nor-cal reminds me of se alaska, i need sleep...maybe this is just a bad dream.....nope, ok just kidden it took me 5 minutes to write this i,m a bright one.....thanks for the help.....peace...