1st timer here. What's causing these light green spots?

My TS1000 lights was maybe placed too close to the plants - I have moved them up higher now. Otherwise I dont know. Googled a lot but im really not sure what this is. Im following the nutrients schedule provided by my local grow shop. Topped all the plants a couple of days ago.
I have 3 other plants in the same tent. 2 are looking great while the third is developing very dark green leaves that has started to curl quite a bit recently.
 

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I water until runoff then wait until the soil is dry 5 cm down which usually takes around 3 days it seems.

Could this be caused by splashing when watering?
 
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