So the ppms are now hitting 1350.

Could my light be too close to my plants? The bulb is about 20 inches from the canopy, it's a 600w HPS. Is that too close? Can heat stress cause the lockout and resulting def that I am now seeing? The amb. temp doesn't get above 80 in the daytime, does that not matter?

Thanks!

EDIT: I haven't mentioned it yet, but WH mentioned ph problem. The ph hasn't been out of the range of 5.6-6.0 since the last time i did a res change and the ph dropped to 4.0 for about 30 minutes while I was adding nutes to the reservoir. Could the ph at that acidity for the relatively short time cause a lockout? I am adding my RO water into the res, then adding the nutes, then adjusting ph. Should I measure out nutes in 5gallon jugs instead of pouring tablespoons of concentrated nutes into my res?