ANYONE GOT ADVICE?

Some leaf tips are starting to go turn a brown/black on the edges. Doesn't seem to be spreading TOOO fast or anything, but def something I want to take care of ASAP. From everything ive read im thinking its either a potassium or magnesium problem. What do ya think?

Using miracle grow moisture control soil
Plants have been growing outdoors since germination, about a month now. Havn't used much for feeding, first sprinkling of miracle grow all purpose (24-8-16) at a very diluted (1/4 strength, if not less), about a week ago. There was slight browning but not much prior to this.

Anyone have any ideas? Im still browsin the threads but can't find a definitive answer..any help would be appreciated

thanks!

Looks like a micro def.

Dont worry about it ,looks like some minor burn from the soil.

Thanks for the advice. Last few days it seems growth has slowed and one leaf has formed a blotchy brownish red discoloration on the leaf tip. I've been a digging through the boards trying to find an answer. Still not sure. N e ideas?