I'm a new indoor grower and have recently noticed an issue that I can't quite identify. I've been growing 2 different plants in soil, White Widow and Mama Mia. The plants grew very well during veg and are currently about 2.5 weeks into flowering. Over the last week I have noticed black spots develop on many leaves of the White Widow plant. Over the last few days, the spots have increased in numbers and leaves with the spots have noticeable leaf yellowing. Leaves without the spotting look fine and healthy. Besides a plant disease, the only deficiency I could image this would be is a calcium deficiency...but I have been giving them low dose cal/mag and using local water which should have ample calcium. We did have some gnats in the tent, which I have since eradicated with fly tape. Not sure if this is related? The Mama Mia is completely unaffected and has perfect color and no spots. Both plants are fed/watered identically, which up until now has not led to any issues. I have been feeding at about 3/4 recommended strength and have not to date had much nute burn.
Fox Farm Bloom
Fox Farm Grow Big
Fox Farm Tiger Bloom
Fox Farm Boomerang
Botanicare Liquid Karma
Fox Farm Ocean Forest
5 gallon pots
Watered 2 times weekly till runoff
Soil pH at root = 6.6
pH of nutrient/water added during each watering = 6.5
2x VIPARSPECTRA Reflector-Series 300W LED
1x iPower GLFANXINL4FILT4M 4-Inch Carbon Filter/Fan combo
Small fan inside tent for air circulation
Humidity is currently around 45-50%. I have slowly been decreasing this leading up to harvest time.
Temperature is maintained around 70 degrees.
Any ideas on what I should do next?
Please let me know if anything else needs to be elaborated.