Noob need help

In need of help the problem is one of my plants, which is 15 days old i guess, has white or grey color tips on the smaller leaves. I dony know wat kind of strand it is because i just got a couple of free seeds from my friends. I've been growing it in MG potting soil, watering it once mayb twice a week, and its been getting direct sunlight. So whats causing the tips to turn a grey or white color? Is the problem dangerous to my plant? And what do i need to do? i have pics of said sprout and i know they suck bc i was taking them w/ my phone and prob only one is good but pls help.

Its the mg potting soil burning it.

damn so its a nute burn do i need to fix it or can my plant live???

flushing shouldn't hurt, ph would also be good to know for water and outflow

if you have to start again, flush the MG before planting, it will burn young seedlings otherwise

growone