72 for res temp is a bit high, should be under 70 at all times. Mine stay between 66 and 69 and only once reached 70, you might want to try and either get more air flowing around your buckets or covering them like me with the white/black backed plastic to avoid the black pulling heat into the res, its almost like a bib on my buckets lol.
My plants are about 3 weeks old now and I had the same thing appear, in my case it was nute burn. I put in a recommended dose as well for seedling, when really i should have done 1/2 to 1/3 of the recommendations. I did a res flush and change, then topped up with 1/3 nute recommendation and the spots stopped appearing, the old leaves are damaged and cannot come back so i cut them off so the plants stop trying to repair them.
Problem with nutes and recommendations in my experiance is every strain is different. i have 2 automara II and one Senis Star, the automara's took the recommended nutes with no issue but the seni got these same spots.
By no means am I an expert but my plant showed the exact same thing and the flush with a reduction in nutes fixed it.
I think going forward for me its always best to start low with them and very slowly move up 100ppm or less at a time with each res change
Other then the spots your girls look great! I hope this helps you and your girls!