What could be causing this leaf problem

Im growing aurora indica (femd)
She is 3 weeks old and im getting ready to start 12/12
Im using ocean forest soil and FF nutes (trio)
400w hps from start
Temp stays in 70s

Im growing three auroras. I havnt done anything different to the three plants but each plant has reacted very differently. This is the particular plant im wondering about. If u have any ideas please let me know. Thanks a lot.

Looks like it could be salt build up, flush and no nutes for a week.

thanks for the tip i water tomorrow so i will do!