Rust spots in flower

I looked at your diary: you seems confuse mate these are not Autopot. Autopot is a DWC system sold in kit. You are doing a classic soil grow, with a very limited % of your soil being hydro substrate, at these proportion they are just right for aeration =). So what is your base soil made off? You could be under feeding.. Are you using a drip system? You could try to up your feeding. After looking at your data, your EC sure looks on the right target but most of it is supplement. Up your base nutrient (bloom, grow and micro). If the other 4 plants don't like it, you will have to find a middle, or hand watering those 2 with stronger solution. on your diary you explain how your light is not uniform, explaining you will let grow the plant in the back. But mostly you talk about *the leaves who gets the best PPFD* showing the worst symptoms: this is normal as light is motor of the photosynthesis equation. (The real food is your light). With extra light, leaves need more minerals to keep up the growth.