Leaf brown spots

Mayb need some Cal mag

Lower the EC (food you are giving them)

Brown spots can be a bit tricky to diagnose without more details, but let's try to figure it out together. Since you've ruled out nute burn and you're using Happy Frog soil, that's a good start. A few possibilities come to mind: Watering Issues: Overwatering or underwatering can cause stress to the plant and lead to leaf issues. How's your watering routine? Pests: Have you checked the undersides of the leaves for any signs of pests? Sometimes tiny critters can cause spots. Environmental Factors: Changes in temperature, humidity, or light intensity can sometimes cause stress and result in leaf discoloration. Disease: Fungal or bacterial infections can also cause brown spots. Keep an eye on the overall health of the plant. pH Levels: Check the pH of your water and soil. Improper pH levels can affect nutrient uptake. might want to provide more details about the environment, watering schedule, and any recent changes. That could help narrow down the possibilities.

As someone who uses Happy Frog soil regularly, I can tell you with you being on Week 3 there are no more nutrients in the soil it's gone by week 3, which means your plant is now telling you it needs calcium, the spots are a sign of a calcium deficiency.

I had a look at the spec's on your grow situation. Right off the bat the first thing i noticed was your numbers suggest a high VPD number. High VPD translates to elevated transpiration in your plants. This causes them to uptake more water at a faster rate which may not sound bad, but remember they also uptake more nutrients than they can handle which can cause all kinds of issues including calcium deficiency due to a lock out. People are quick to chalk necrosis up as calcium deficiency. In reality, there's plenty of Calcium, it's just locked out. In veg your VPD should be low. Like ideally, 0.85 to 0.95 All those numbers translate to are low temp + high humidity = Veg 0.85 to 0.95 example: 75F / 75% RH In Flower your VPD should be higher, like 1.25 to 1.50 Low temp + lowered humidity = Flowering VPD 1.25 to 1.50 example: 75F / 50% RH These numbers are really important to get correct and keep correct. They determine the rate at which your plants grow and their uptake of nutrients in relation to what they can handle. If your VPD isn't dialed in your can have all kinds of growth problems like lockouts, toxicity, frequent watering, deficiencies.......it's important.

Either the plant needs a bit more calcium or you may have had water droplets on the leaf and the light then burnt it.