Yellow spotting on the base of newer leaves

Plants are about 3 weeks from seed indoors in 12oz cups of canna brand coco being fed 5ml of hesi rooting complex and 2ml hesi tnt , and hesi supervit 1 dropped per gal of water. Fed every other day. Under a 6 bulb fluorescent light. 3 of 15 plants started in early august show this.

Temps in mid 60s to low 70s.

Heres another shot a day later

spider mites?,, they make small dots like that, look under the leaf with a loupe or magnifier glass,, you cant see them with the naked eye