Yellow leaves with spots

Hey everyone,

Im running a single plant NFT with 3 gallons in the res. ( this is an experimental setup)PH is 6.1 ppm 1100 day 30 flower not sure what the strain is. 600w hps 75% and FF nutrient line...just grow big big bloom and tiger bloom. Im out of town and my caretaker found a few of the larger fan leaves around the top of the plant looking like this. Rest of the plant appears to be fine. Anyone have any suggestions?

Thanks everyone i appreciate it.

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