This is a cal/mag issue and you're going to need to flush since you've probably got a lockout. Run 3x the amount of water as the pot size through her (so if you're growing in a 3 gallon, you'll need to run 9 gallons of ph'd water through her adding some cal/mag with the final gallon of water). Make SURE the PH of both the water you flush with and the runoff water is between 6.0 and 6.5 (6.3 is the "sweet spot")... the PH of your runoff most likely won't be anywhere near that range when you first start the flush - and that will confirm the cause of your problem. Let the pot dry out completely before you feed again - and every time you feed/water, pay attention to the PH of what you're giving! You'll want to let the water/feed sit for about 15 minutes before you measure the PH as it will change over time... once you check it, you can amend it up or down as needed. Don't expect the leaves that are affected NOW to improve... they MIGHT get a LITTLE better - but don't expect it.
Good luck! It's easily solved if you follow those steps!