HELP! Seedling in pot outdoors showing bad burns

[PlantMatters]

Over the past 3 days my week old seedling has developed bad burns on the edges and tips of its first 2 sets of leaves, the first signs of stress were drooping of the leaves. The strain is Cookies Kush. The plant sits outside on my terrace and gets about 8 hours of direct sunlight a day. The medium is generic potting mix from the garden store. I have been feeding with 6-7 ph water that has had a chance to evaporate the chlorine.

My main suspicion is over watering but the symptoms are getting worse even though I have allowed the medium to dry out. Could this also be caused by the sun? I'm in Spain and the temps have been getting up to 27 deg C last few days. I have also read about wind burn and I do get a bit of a sea breeze in the afternoon. Only other thing I can think of is some nutrients in the soil that I am not aware of burning it.

Thanks for any help, my plant was looking so healthy before this so I am very keen to sort it quick

[Toker1]

Few things. First off... looks like pests to me. Maybe a bit of nite burn too. Put up some yellow sticky traps to catch the adults. Then examine the traps to see if you have an infestation. Find out what kind of bugs they are and then plan an attack on them with a predatory bug that will feed off the infestation.
Second, I don’t know how water treatment works in Spain, but here in the US we don’t use chlorine gas to treat water any more. The gas was too dangerous to be around. So chlorine will not gas off of modern day water any longer. The only way I know to remove chlorine from modern day water is mechanically like filtration for example.