Random few leaves dying

They are about 2 months old and they just started to turn. I tried looking at pictures of different deficiencies but I can't figure it out. Please help first grow. I use proper ph water and ff grow big nuits, they just got put under a 400 mh could it be burns? The dying leaves are mid way down to lower section.
 

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The general hydroponic basic test kit. I know it's not the greatest, but I haven't had any issues until now and my 3 younger ones are ok. I did research about the three leaves and they said that it happens with some OG's. They're in fox farms ocean forest and a touch of all organic miracle grow soil. Been in same soil for a few weeks without a problem.
 
URBAN GARDENER : I found a site on International Cannagraphic with the whole rundown on deficiencies with pictures, it might take a bit to find the right spot. I hope this helps.
 
I don't currently have a soil tester, I thought Ocean Forrest was good how it was. I use the General Hydroponics ph control kit for the water.
 
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