issue with my plants leaves

So last monday into tuesday i switched my plants into flower, starting around friday, some of my laves began to become blackish. a few yellow and black. I have two white widow plants and for some reason its only happening to one of them. the other one is perfect and not one of the leaves are having an issue. i was feeding them half a gallon of water with 2g megacrop every third day and every third watering i would use only water no nutes. Since putting them in flower ive upped it to .75 gallon of water and 2.5g of megacrop which is below the dosage it suggests as reading on here alot of people said to be safe just go below the recommended in many threads. anyone have any suggestions? should i up the dosage of megacrop? is it calcium deficiency?

any suggestions?

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Matt what's your Ph? How big are your pots? Are you watering until there is runoff?

It doesn't look like nutrient burn, more like a nutrient deficiency.

Click on this chart to enlarge, use the magnifying glass once you enlarge.

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How far away are your lights? I noticed the fan leafs are burnt and curling up?

thank you @Hobbes thats an awesome photo. i feel it could definitely be quite a few options of those. my ph is around 6.5 ~ and im using 5 gallon pots. I usually water with 3/4 of a gallon of water with 2.5g megacrop. I think i am going to up it to around 3.5 since that is the recommended dose, i just always under feed cause alot of ppl in the megacrop threads say feed with less until you think the plant really needs it. im using fox farm ocean forest. Its hard to say if i water until runoff because i use fabric pots and alot of the time the water leaks out the sides of the pot as well.

@Ganjamandan77 my light is 28-30 inches from a majority of the plants. recommended on the website for my light is 24 inches.

the most confusing part of all of this is like i had said i have two white widow from same website, same purchase and its only happening to one and not the other and i do everything for them the exact same lol

thanks for the replies i appreciate it

i fed with 3.5g last night so we will see tonight if the leaves are any better