leaf tips curling and yellow spotting. Copper deficiency or cal? or neither

Pineapple express and kalashnokova autoflowers. 16 days old from germ.

Under 2 600 watt hps 3 feet above canopy.

Temps stay between 75 and 85 during day time and 65-70 at night.

water with ph. 6.4 RO water and using roots organic soil.

I have for the last week tips curling and yellow spotting on mature leafs. And today one tipped turned dark greyish looking and very brittle.
I though originally that they were overwatered so I didnt water for 4 days to let things dry up and I watered on the 5th day (last night) and took pics today.

Also I have been treating plants with Azamax once every seven days and they have only been treated twice.

Will provide better pics tonight.

i havnt used hps yet to grow thats actually going to be my next grow but what i do know is that young plants don't need as much intense light close to them even with CFL's I give my seedlings some good space until they start to stretch to the light then i lower the lights to them. so if i were you i would keep on the same watering schedule you've been on but pull the light back a bit further and see if that helps

new leaf sets are curling down and shriveling. seems to get better for a few days then worse.

lost camera cant get better pics at the moment.