G'day maspino1,

I have a limited knowledge on this, as I am starting my research in this area...

There are many variables you need to consider when diagnosing problems eg: Young leaf, old leaf, stage of growth (Age of plant), environment, mediums, etc...

Appears you have had a combo of - deficiency and perhaps PH issues, though the turning down and browning of tips can indicate nutrient burn but, this can be normal for older leaves nearing harvest (Old leaves will turn yellow and eventually drop off). Here are some systems/reasoningā??s relating to your post:

1. Yellowing of lower leaves = Nutrient deficiency (dependent on age of plant?) and or PH too low and water is acidic
2. The turning down of tips and browning = Nutrient burn
(Turning up of tips and side of the leaf and evedince of browning = Heat issue)
3. Mature leaves turn yellow and edge areas turning dark grey = Nutrient deficiency OR just old leaves dying (There are slight differences you need to know)

Hope it helps a little...

Cheers!