neut burn problem but....

Hi i have neut burn on one of my plants and its effecting some of its leaves. The big problem is its only effecting one of my 4 plants

It wouldn't be so bad if i wasn't using hydro system but because i am i cant change the water to suit one plant because the other 3 will suffer....

Am stuck on what i can do

any ideas on what would help

I don't understand how nute burns affected one single plant !

what else could it be that looks like nute burn but only affects one plant?

also could be cal deficiency as it looks more likely a cal as it the pics iv seen match closely but still why is one plant near dead off it and others are fine....