bros please help diagnose these leaf spots

what we have here is a fast buds crystal meth plant, maybe 45 days old, started developing spots on the leaves a week or so ago, started on the top fan leaves, of course there are only a few of them anyways :biggrin:

• promix soil
• 1k hps
• 18/6
• 70(night)-74(day)F
• ~40RH
• Water ph 6.3-6.6
• nutes: fox farm trio, cal mag, big buds
• not overwatered
• other plants are fine, tho different strains
• some of the bottom leaves are yellow from LST close to the soil, no problem there
• http://www.worldwide-marijuana-seeds.com/products/fastbuds-crystal-meth

Looks like calcium def

How much and how often have you been adding the calmag?

I cal mag 3-6ml gallon on most waterings, so maybe every 3-4 days and I bumped it up when this showed up