1/2 - 2 weeks old plant is getting brown leaves (In the middle) (Pictures)

Hi

I have 3 white widdows, around 1 and a half 2 weeks old. First it started with one of the plants, small white cracks in the plant, then they became bigger and started to getting brown. It started on this plant and slowly spread to the other leaves and now it has started on the 2 other plants

They are grown from seed, in normal soil i have bought (without fertilizers)

Looks like a deficiency bro. A cal/mag sup will do it, eventually that leaf will be dead. Its not a true node and its just blocking air flow imo, when you start lsting(if you do). The two white spots in the brown spot look like bleaching from heat.

I can not see anything in those fuzzy pictures.

What water source are you useing to water your plants? Are you useing tap water? If so you should have plenty of Cal and mag.

I have been watering with just tap water for years. I truely think it is all hype about how you have to use R/O water or allow the water to sit for 24 hours. People have been growing plants for decades with plain tap water out of the hose. I am sure the people with 200 plant crops do not use R/O water. at 3 gallons wasted for every 1 gallon purified . They would be useing freaky high amounts of water.

I use tap water, but here where i live there is no calcium in the water. So i will give them some and hope it helps I had heat problems in the start, and they where hanging with their heads. But i fixed it in time, and they are doing well except the brown thingy there.. I'll try take some better pictures

What's normal to you may not be normal to me. What brand of soil?
This could be abnormal soil but faking it~
I think it's the soil!