Hey there man. 90+% certain you're looking at the beginning of P/Cal/Mag deficiency. I had a touch of septoria and it's comes in more as circular blotches (like a burn mark, burning evenly from the center of the spot, outwards. This specking is consistent with a Cal deficiency, but I say P/Cal/Mag because they go hand in hand. When you see a Cal deficiency there's a hell of a good chance it'll follow up with/already have a Phosphorous Deficiency.
Your parameters are all good and/or adequate and definitely don't believe this is a sign of light burn, either. Up that P/Cal/Mag for your next feed and either hold/slightly reduce N/K (this is up to you) and within a week this will stop... The affected leaves may have to go eventually, but spread should indeed halt. Good news is, these are very early signs and it won't take any time to knock it out and balance your feeds to address her needs. Finally, if you feel nervous about leaf septoria, you may remove the affected leaves (as recommended) carefully and look for any new signs of localized spotting. Also, air circulation is key. Keep everything moving and septoria won't have the ability to form and spread.
This all being said, I highly, HIGHLY doubt septoria. Good to take the precautions in avoiding it, but I do not believe this is what we're looking at here. Cheers man! and good luck in the coming days and the next feeding. Drop me a line if it doesn't get better, spreads or you want more info on the deficiencies' and plant symptoms.๐๐(including remedies')