The lowest leafs of your plants will die first. This has nothing to do with deficiencies or burns, its rather a natural effect, because the lowest leafs will get less sunlight which results in less photosynthesis -> yellowing -> dieing.
Don't be worried about this mate! :-)
As for the last few waterings only ph of 6 and teaspoon of epsom salt per 2 liters, i will soon be getting an ec stick as i don't have one, i will check the runoff ph and see what the ph is like, thank you.
Looked at you diary. Are you still feeding grow to your girls?, you shouldn't be at this stage. Are you feeding at ph 6?, increase to 6.2 then 6.3 in a week. Check your runoff ph and ec levels to see where your at and react where you need to. Cheers