first time grow need help!

my girl is almost 3 weeks old i have her in mg organic soil mix 10-5-5 and mg perlite, the problem is she has older leaves that are turning yellow it started from the tips(i think its nute burn). i want to know what i should do any help or constructive criticism is fine it would be appreciated

post up some pics if you can. are you adding nutes of are they in the mg soil already?

i can't find my camera cord so not able to load up pics, but nutes are already in the soil