Well you could add some mg and see if it helps or hurts. I think it's bugs. They're not on your plants 24 hours a day....especially white flies which come and go. You say you are seeing one thing but the symptoms are showing another. You have to go by what "the evidence" is as they say in the forensics world.....just because you personally haven't seen bugs doesn't mean they aren't there.

Here's a guide so you can look through different symptoms and perhaps it will help you decide.
International Cannagraphic Magazine Forums - The Complete guide to Sick Plants,pH, and Pest troubles!
Weedhound Reviewed by Weedhound on . Plant Problems For First Time Grower Can anyone help me diagnose my plant problems? One of my plants has some yellow spots on its lower leaves. I transplanted the seedlings about one month ago using Miracle-Gro Moisture Control soil. The plants have been under 24x7 light since seedlings. I have only used Miracle Gro's All Purpose Plant (24-8-16) Food once about 3 weeks ago. I would gladly appreciate any replies. Thanks my fellow growers. I have: 2-plants 1-Fluoro light fixture 2-45watt cool white bulbs 24x7 lighting Rating: 5