Problem in my cultures and I can't find what they have.

Overwatering. ur soil is too compact/clayish. The top is drying, but u maybe not measuring the first 5 centimeters of soil to check how umid is there. fert is already too much for this stage. wait for ur plant develop more leaves and wait to water again. Stop watering, these symptons are overwatering, burned leaves of ur plant trying to breath on roots. U probably do better with a mix of coco than actual soil. Look for other symptons before u water next time - like - the leaves will droop down when they need water, different from pure coco or half mix coco, the ph will not change drastically by waiting untill the plant ask for watering. At this rate, u will probably water 1 week at time, doing 5% of the total volume of ur pot (if u have 10 liters pot u will water 5% of it , which is 500ml) at week. when they grow like for or more big leaves and show more new groth at stem, then u can water more times at week and following the "dry soil criteria".