Rusty Leaf Spots

Ok I just transplanted my ladies at 20 days into larger pots.
Next day I changed lighting to 12/12

This is a CFL grow.

Tonight I noticed little rust colored splotches on a few leaves of one plant. All other plants doing fine. Just this one.

Any help appreciated. Pics attached.

what kinda soil you usin ?? im gonna jump out on a limb and say its miracle grow ?
how about nutrients ?? how often are you watering ?

Do you mist your plants with the lights on?? If so you may have sun spots which is caused by leaves having water droplets on them and the light magnifies them and they burn your leaves. Hope this helps.

My original potting mix was

50% Ocean Forest
20% Sunshine
15% Periculum
15% vermiculite

I just transplanted into bigger pots. Nute store was out of Sunshine Mix and Vermiculite so I mixed 80% Ocean Forest and 20% Periculum.

I am just barely starting to use nutes. Grow Big. 6 days ago I added 1/4 tsp per gallon instead of the 1 tsp per gallon in an attempt to easy my plants into it.

On day of transplant I used 1/2 tsp per gallon.

I water every 3-4 days. I make sure soil is dry to determine if it is watering time. Today the soil is pretty dry so I am going to water before I go out for the weekend. I plan on using Grow Big and adding a half of recommended dose of the big bloom since I started flowering stage.

I checked today. The spots aren't too much worse (they haven't taken over the plant or anything) and its still only on one of 7 plants.

Perhaps it is from water dripping on the leaf.