need some help with plant problem

Hi Everyone,
I need some help with my mother plant.
It started in the lower older leafs, with the edges looking like the upper ones, then the leaf slowly turning yellow, with the tip turning brown.
Hope that's enough info.
If you have anymore info needed to help solve, let me know.
I'm thinking mag. Deficiency?
What do you think

one thing i learned is before checking any deficiency, especially rare ones, check the ph first....and dont do the same mistake as me, check the runoff water ph and not the water before it goes through the soil. If its ok, then check this table it might help: http://www.amsterdammarijuanaseedbank.com/Growguides/troubleshootingsolutions/nutrient-table.html

Hey Choufleur,
Thanks for your reply the link in awesome!!