Help identifying these weird spots!

Howdy!
My girls have had these weird brown spots since about week 2 of veg(they are in week 6 of veg now) i switched from FF to GH in week 4 and was amazed by the new growth in the GH but the brown spots still came. It is RO water and i am using cal/mag 5ml per gallon the smaller one is in week 3 with no brown spots....
as you can see its a simple dwc set up.
PH 6.1
GH flora series ppm 850 300 ppm for the smaller plant
Mars hydro ts3000 at 30”
19x19 grow space temps range from 85-66 at night if its cold (ac kicks on at 85 to cool to 78

4 different strains
Thanks in advance!
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