mg def or nute burn?

ok so my plant is fairly healthy but recently i noticed that my bottm leaves were yellowing which slowly progressed to dying edges and necrosis, the shoots on the stem at the same node is still fine but it appears to be slowly getting higher, what is this? i have soil with a small amount of slow release fertilizer in it (the suspected culprit) but i need to know what to do. i will try and get pics tommorow.
cheers guys
chazz

leaf yellowing could be Mg deficiency but you are right in that it is most likely nutrient burn - especially combined with the leaf necrosis.