Everybody is always talking about nutes but nutes role in grow success is less than 10%, the key is the environment for transpiration!
They like warm environment, lots of light and usually small amounts of nutes (strain dependant). And keep your roots in good condition.
So what kind of temps...
What is your RH? 25-28c temps should be perfect unless RH is below 50%.
Other thing you might try is to raise your PH to 6.0-6.1 so it can absorb different nutes better.
I had septoria one time indoor when there was NO ventilation.
I'm pretty sure this problem is due to low PH causing cal lockout as buyyouabeer said above