Leaf septoria?

hello man, i think that is a beginning of a Mg deficiency. Your humidity level is perfect so is very difficult that can be a septoria. Good luck mate :)

Leaf septoria is highly doubtful - but you can read about that fungus here: https://www.ilovegrowingmarijuana.com/growing/marijuana-diseases-leaf-septoria/ I think you're right in your assessment of calcium deficiency - but it's only just starting and I don't see the need for a full flush... If this were my grow, I'd back off on the amount of your Rose & Flower nutes as it contains a lot of nitrogen which may be causing a lockout of the calcium... I'd also add some calmag to your nutes but do this only once a week. If the problem gets worse, then you may have to do a full flush but right now, the problem is only a minor one. Nice job on the scrog and lollipopping, btw! Good luck....

Magnesium deficiency, not calcium or leaf septoria. No need to flush, just add some (or more if you are already using it) cal/mag and/or epsom salts into your feeding routine.

High Catova, This is a starting calcium dificiency indeed. Calcium, magnesium and iron deficiencies often appear together. The best way to restore is to flush your plants with clean pH 6.2 water, and then resupply the water nutrient solution. You can also supplement your nutrient-water solution with Cal-Mag to avoid calcium and magnesium deficiencies in the future. You can do this flushing by slowly pour water pH 6.2 onto the top of the soil, allowing it to drain freely from the bottom of the pot. Pour slowly, so the water doesn't overflow from the top of the pot. Use approximately four times the pot's volume in water to flush the soil. For example, use 1 gallon of water for a 1 quart pot. After the flushing you need to let the soil (almost) dry out completely. From there you can start giving water with pH 6.2 and nutrients but do not exceed EC 1.8 Happy Growing! 😋