Need help 5 weeks into flower leaves dying

[Wwgrowhelp]

I'm using fox farm ocean Forrest soil
5 gallon pots
Fox farm 3 part nutes
And just added cal mag to try to fix issue
I water every 2 days with 5 gallons 11 plants
2 600 watt 8 inch exhaust fan for lights and filter
6 inch intake fan for fresh air
Leaves are changing color and getting brown spots in the middle of leaf
Then they start to curl and dry
Please help

 

[waknbak88]

Can you upload a pic of the whole plant? And what is your feeding schedule look like. I deal with this issue and it is usually a potassium or phosphorus problem, and usually cause my ph was too low. If it's the oldest leaves then you are probably fine.