I have some yellow spots as can be seen in Week 3 ...

Magnesium Deficiency The lower and older leaves start turning yellow between the veins when a cannabis plant gets a magnesium deficiency Problem: A light green or yellow coloring will begin to show on the veins and edges of the lower & older leaves – this is one of the classic signs of cannabis magnesium deficiency. Magnesium is a mobile nutrient, which means that the plant can move it from old leaves to new leaves. Solution since you have cal mag check ph make sure it's between 6.5 and 7.0 cuz too acidic magnesium can not be absorbed

Hey Steve, I know everyone's chiming in on this already, but I'm growing fast buds with almost identical symptoms. And i narrowed my problem down to 3 things I believe. First I had a habit of misting my plants with water and it not having the chlorine evaporated out and letting it get to much light when wet. I also had to reduce my light hours on my LEDs from 20 down to 18 and raise them slightly (i also heard sometimes the plants demand for cal/mag/potassium go up with some light intensity), and last i made sure to stay on top of more calmag supplement. I always thought my tap water had enough calmag in it but it's just not true for certain strains or conditions. I haven't seen any new leaves affected since then. Happy growing

Your plants look like mine do when I don't add enough calmag to my feedings. If it progresses the yellow spots will turn into a more rusty color and the stems will get more pinkish purpley red. Before you add calmag to your feeding schedule, I noticed you haven't listed the PH of your water. What is the PH of the water you are feeding your plants? You want the PH of your water to be about 6.2-6.8 and it is fine if it varies a bit in that range. If its too high or too low you will wind up locking out nutrients and that might be what has happened here. The reason I think it might be a PH imbalance is that it is not super often that soil grows need an added calmag supplement. The only reason other than PH imbalance that I could see there being an issue with calcium and magnesium would be that the soil is low quality or the plant has used up most of its nute reserves and needs to be fed. Next time you water make sure to get some runoff and catch it. Take the runoff you caught and test its PH. If it is outside the range of 6.2-6.8 then that is likely the reason for the discoloration. To bring the ph back in line, flush the plant with PHed water until the runoff ph is back within the proper range. This will reset the medium and allow the plant to start taking up the nutrients it couldn't before. If you dont have a PH meter already, I highly suggest getting one as they are an invaluable tool for growing weed and troubleshooting issues. It is also very possible that now that you are using nutes there may be enough calcium and magnesium to fix the issue. Keep an eye on the new growth as old-growth won't repair itself. If the issue persists after doing everything I mentioned then I would add some calmag to your feedings. Good luck!

You have a Calcium issue ( little brown dots on the leaves) and a magnesium issue ( purple petiols on the leaves). Add some extra cal mag from now until flush a d it will be fine , the affected leaves will not recover but the need growth will be fines