lower leaves yellowing could definately be a N def, BUT those rust spots might be another def or nute lock out in general(over fert or PH lock out). Which leads me to believe you need to check your PH asap, watering water and runoff. Plus if you have an EC/TDS meter measure the EC/TDS of the runoff water and post that also. I do beleive the leaves curling down like that are low PH/over fertilizing. Alot of times they go hand in hand, since alot of nutes lower the PH. And too much will drag down the PH.
I think feeding everytime you water is too much and might have created some salt build up.
If you don't have access to any meters give it a good flush with medium strength nute solution and that should replace the old nutes and replenish the medium.
observe until next watering, see how she reacts.. add more if nutes if she's still yellowy but watch for those spots again.
I've had it before where I was watering with 6.8 but the runoff was coming out at like 5.6-5.7 which means my PH was lower then 5.6 probly 5.0 maybe in the 4's
I had to flush and water with 8.5 PH a couple times to get it up. and I still had to fight with it till harvest. mind you they turned out nice anyway but I missed out of some potential.
