Whats wrong with this guy?

Can anybody tell me what is going on here? This is my first grow and one of my plants seems to have some sort of deficiency. I think its a P deficiency but am not sure what do at this point. It has started on the bottom leaves first and begins with brown spots on the tips of the leaves moving inwards. They then start yellowing, necrosis, leaves curling up. I have attached a few pics.

I recently upped my nutes from 600ppm to 750 and then 900ppm over a 24 hour period to see if that would make a difference. Im not sure if those leaves are even salvageable at this point. Any input would be appreciated.

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How long has this problem been going on? 1 week

Are you growing in a PVC grow tent? (example: Hydrohut or any other non brand tents) NO

What system are you running? (DWC? Ebb flow? Aero? Water Farm? Flood Tables? and so on...): DWC

What STRAIN are you growing? Problem Child is Critical Jack

What was the establishing technique? (Were the seed or clone?)Seed

What is the age of your plants? 3 weeks
How long have they been in there mixture they are in now? (coco,soiless etc..) 3 weeks

How tall are the plants? 8 in

What PHASE are the plants in? (seedling, vegetative or flower) are the plants in? veg

What Technique are you using? ??

What substrate/medium are you using?(Hydroton, RockWool etc.) Hydroton

What is the Water temperature? 68

What color are your roots? White? Brown? Are your roots slimy? White and not slimey

What Nutrient's are you using?(If growing soiless) Lucas Formula

What is the TDS/EC/PPM you are usin g 900ppm

What is the pH of the "Tank"? 5.7

How often are you testing your pH/PPM/EC/TDS? twice a day

Are you sure your calibration is correct on your equipment? 90% Im going to recalibrate today.

What size bulb are you using? 175w MH

How old is the bulbs you are using? Not sure

What is the distance to the canopy? 1 foot

What is your RH Factor(Relative Humidity)? 43-48%

What is the Day/Night Temp? (Include flucutaion range) 77-83 deg F

Is the fan blowing directly at plants? Yes
Is your water HARD or SOFT? Hard but I mix 50/50

What water are you using? Reverse Osmosis (RO)? Tap? Bottled? Well water? Distilled? Mineral Water? Distilled and Tap

If using tap water, what is the ppm/EC/TDS of the water right out of the tap? 500ppm roughly

If using RO,Distilled,mineral water, what is the ppm/EC/TDS without any additives? 8ppm

Are you using water from a water softener? No
Has plant been recently pruned, cloned off of or pinched Pinched the other day

Have any pest chemicals been used? If so, What and When? No
Are plant's infected with pest's No