Brown dry patch

Could be anything ph fluciation small cal mag deifancy though it would probably create more problems trying to solve it than it would do just leaving it. I see that the medium looks quite wet I wouldnt advise watering the whole pot at this stage only around the base of the plant shes only small she doesnt need much and with alot of perlite you will hold onto alot of water and could cause an overwatering symptoms to arise im sure if you just carry on doing what your doing but less of the water and only water her when the medium is completely dry that way you know shes taking up as she should. I finish with what i say all the time on this site when it comes to seedlings they are very tricky to work with too little and they wont grow as quick too much and youll lock them out so they slow down completely its very common to have spymtoms like these and only really experienced growers can keep a seedling green or a plant green through the whole cycle its just something that comes with trial and error and most of all gorwing experience and you will get there everyone does you just haveto find the right remedy for seedlings and repeat it any way im sure youll do great best of luck :) 👊