Brown spots - Critical 2.0 auto

Sorry my poor English but I'm not a native speaker.
I'm also a new grower and this is my first attempt to grow indoor:

Box: 30x30x80cm home-made (11"x11"x30" inches)
Pot: 9L
Light: 4x15w Led bulbs (6500K) + 2x14w Led bulbs (2700k)
Soil: Atami Bio Grow
Fert: Bio Bizz (Grow & Bloom), Aptus CaMg Boost
Air: pc fan output + pc fan inside the growbox
pH: 6.5
Light cycle: 20/4

So, I've never fertiled the plant until the flowering. Then i started with the BioBloom suggested doses and a little bit of Biogrow (just 2 times). When the plant started to show these brown spots i was doubtful wheter it was Ca/Mg deficencies or some heat/light burn.
So i bought the Aptus Ca/Mg boost 1 week ago and i also moved the lamps but the situation on the leaves remains more or less the same. Today it's 34 days from seed.
Does anyone have an idea? How does my plant look like?

Since you said you havent fertilized till now,Id suspect a low amount of nutrients in the soil.If the ph is good,they likely need more nutes.You can either guess at what they need or get a soil test kit and know what the problem is.Ive used alot of fertilizers over the years and some of them are very weak.I suspect this is to prevent people from nuking their plants.

PH should be at 6.0 and lights should be closer, feed at 75% of full strength.