upper leaves yellowish spots

The spots on the upper leaves may be due to nutrient deficiencies or light stress. Your soil has low nutrients, and occasional CalMag alone might not be enough. The light intensity and distance seem safe, so light burn is less likely. A flush isn’t necessary yet unless you suspect salt buildup. Start feeding with balanced nutrients and monitor the plant’s response.

At first glance, the values all seem to be fine. However, I would recommend slightly lowering the pH to around 6.2 – not necessarily because of the spots, but as a general measure to improve nutrient uptake. As for the spots, they could be early signs of a calcium deficiency, though I consider that unlikely at this stage. Another possibility is pest damage – it would be worth checking specifically for thrips. Alternatively, the spots might simply be lime deposits from tap water or minor burns caused by water droplets on the leaves under light exposure. My suggestion would be: 1. Carefully inspect the plants for pests, especially thrips. 2. Lower the pH to 6.2 regardless of the spots. 3. Keep an eye on CalMag – while a deficiency can’t be completely ruled out, it doesn’t seem very likely at this point. Happy growing!