1st time grow and need help

[cs19]

Hi new to the forums and i have a problem. About 3 weeks into veg and I'm starting to notice a few shriveled dry spots and yellowing I'm clueless.

seems to be bad on one plant and the others just have a few leaf affected. This is my first grow and have been pretty much problem free up till this point.. using general hydroponics nutes and under 1000w hps at 18/6

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[aloni151]

does this happen on older\younger leaves? have you recently increased/added nutes? ph lvl?