diagnose my leaf

I sense two problems in my garden. The first is leaf spotting in the first picture. The second is leaf curl in two separate plants in the next two pics.

I started these from seeds around 3 weeks ago i think. Its a sativa dominant mix. I'm using sensi grow part a&b with a cal mag supplement, all at half strength. I water once every 3rd day for 15 min using a flood table and timer. I was misting 3+ times a day previously with a little nutrient. I have since cut down and taken the nutes out. My ph has been anywhere between 5.8 and 6.2 when i water.

The roots are just starting to show out the bottom of the rockwool, but i want to save my hydroton for the flowering stage unless i need to give my plants more room immediately. I don't have a heating element for my water, the temp has been as low as 18 before when watering, but normally higher. Thanks for any advice, I appreciate it.
 

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