Holes and Brown Spots Help

I have five plants in the 4 week veg stage and they are growing strong. They are in a hydro bubbler system. Ph is around 5.9 to 6.2, PPM is about 650 to 700 the Temp in the room runs about 65 to 70 degrees Farhiet. In the last week they have been getting what at first appears to be like little clear glaze spot that is has been turning brown and last couple of days they get whole in them tips of leaves are curling down and tips turning brown. The leaves at spot have rips like maybe bug, but I don't see no bugs on them. I have not been spraying them so I know it not burn from water droplets, I have anouther room that has my flowering plants and no sign on them. only difference between the two rooms is temp. Is this a nuke problem or bug. Please help don't want to lose them. Bizzy

come on you experts I need feed back? Bizzy

usually when leaves curl down it means lack of nutes, but it sounds like bugs too. check your ph again and check your plant with a magnifying glass closely, check every square centimeter, underside of leaves especially, caus alot of the mites or bugs like to hide there. if it`s bugs, you need to get some insecticidal soap and spraythe whole plant, undersides of leaves too. it`s biodegradable ant wont hurt your plant.
i hope this helps you , it sounds like you know quite a bit already.
it`s good to see a knowledgable grower on here
i have been growing about 20 years, indoor, and i`m still learning new things to help me.
good luck