bone meal, but it's pretty 'hot' for seedlings.
Hm. Sounds like something ELSE in the light warrior/FFOF is locking out micros. FFOF is way too 'hot' for seedlings of many strains, and if your strain is already a light feeder, that's a culprit to look at. Light Warrior has a lot of coco in it too from what I understand.
I'd start seedlings in a seedling starter mix, or Happy Frog with some added perlite, or rapidrooters if you are very cautious. They have the same microorganism as Serenade added at the factory.

That is not actually Black Spot Fungus. That's a nasty disease that affects roses and other thorny cane plants in hot, wet weather.