YES, it looks like a late stage potassium deficiency, imo. Excessive sodium causes the K lockout.
Some products/remedies for K-Deficiency are: Wood ashes, which are fast absorption (but will offset ph), Kelp Meal, which is medium absorption, Greensand, which is slow absorption, granite dust, which is slow absorption. Sulfate of Potash, Sulfate of Potash Magnesia, Muriate of Potash, which are medium absorption. Foxfarm GrowBig Hydro, which is fast absorption. (FFGB can bring your ph down as well) Earth Juice Meta-K, which is fast acting. (Can bring down your ph as well)
Effected leaves won't recover, but you'll see a turnaround after about 4 to 5 days when using a fast acting nute.