Brown spot

holy shit... 10ml/1 is twice the amount that hesi recommends for adult plants. Hesi recommends 2.5ml per liter for young plants (and normally half of it is sufficient, and if not, you can slowly increase the quantity). but in this stage you wouldn´t need any fertilizer... it´s better to wait until the plant shows you brighter leafs for example. by the way.. earth is normally enough fertilized for the first few week..especially if you have big pots like in your case.