from the picture I would say almost everything but most likely all caused by same issue PH
Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so = NA
Strain; Type, Bag seed, or NA
Soil in pots, Hydroponic, or Coco?
System type?
PH of runoff or solution in reservoir?
What is strength of nutrient mix? EC, or TDS
Indoor or Outdoor
Light system, size?
Temps; Day, Night
Humidity; Day, Night
Ventilation system; Yes, No, Size
AC, Humidifier, De-humidifier,
Co2; Yes, No
Add anything else you feel would help us give you a most informed answer. Feel free to elaborate, but short, to the point questions and facts will help us help you smile
It’s difficult to say from a picture. But from i see from the photo, it’s looks like nutrients burns and probably an alkaline soil. Please follow the instructions from @Donaldj and give us some tangible data so we can try to be helpful 
I will try and not sound so abrupt and list off some things that stand out to me from picture if it helps you realize the importance of sharing some details.
Leaves have taco shell Heat stress? Low humidity
Yellowing: nitrogen deficiency Mag Cal P K Iron? any of them could be an option
Drooping? Clawing: over or under watering? Nitrogen tox?
Curling up and burnt: Nute burn? root rot? fungis nats? or P def?
Plants are stretched: too little light too far away or males? Possibly sativa?
We could draw a 100 conclusions on a picture alone if you desire helpful feedback there has to be more information
Thanks heaps will do
That thing has been growing for 2 years?
What tha… f… seriously… 
You should download the free grow bible from this sight… please … lots of good info…
Spider mites ?
2 year grow… i like it
Hope they grow
Into
Some
Dank
Weed , would of been
Cheeper to buy it after you factor in the electricity
Costs 