brown leaf tips in week 3 of veg

Possibly a bit too much light. Nodes look a bit tight. If that is the case, may need more light after it develops a bit more. You give too much too early and they get stunted. the amount of stretch is the guide for light intensity. tiny plant in a big pot is a bad idea. you now have to attempt to water a small column around the plant and increase diameter as it grows. Water all the way down to the bottom. Do not superficially water. You want another intermediary step in size or let it grow out a bit more in the previous pot. If you can't water the whole pot after transplant due to size of the plant and how long it'd stay wet, then it's too small for that pot. Allowing it to dry excessively will only exacerbate what you are seeing, if it was caused by nutes. The plant isn't drinking much, so most of the water loss is from evaporation which creates a more concentrated water-content left behind around roots - again something completely avoidable with proper pot:plant size. so, don't do weird things with watering. You simply water until it's wet all the way down (in a more normal context you ensure the entire pot gets wet), then wait for 1" deep to dry and repeat. Don't deviate from that. Even watering a smaller column will result in very long wait times between irrigations. This is just as bad as leaving irrigationw ater out for as many days -- stagnating and growing weird shit. If this is a 1-time issue, that's not so bad, but if successive irrigations are taking a very long time between, that's when bad things will grow in your substrate. Anything over 5-7 days after first irrigation, i'd consider adjusting timing of transplant... i don't know if that's the 'best' cutoff or not. But, the next irrigation or two will get down to a more normal time frame, so it's tenable. Use more perlite or similar next time. That substrate looks to have poor porosity and drainage characteristics. Anything akin to soil should have roughly 50% perlite or similar and somethign that holds less water per volume, like coco, needs about 33%. This will increase irrigation frequency but ensure the proper gas:water ratio in soil and ensure deeper, healthier roots, which results in better growth.