Potassium deficiency causes damage like that. Judging from the degree of necrosis, there may be a second deficiency like Phosphorus-def at work there as well, but Potassium is the major problem. Get yourself some good organic fertilizers to replace the spikes. Kelp Meal and Maxicrop are decent sources of Potassium, while Bone Meal and high-P Guanos are some of the best sources of Phosphorus. Welcome to GrassCity
You can mix it into any future soil mixes but with your current plants you'll want to make it into a tea for manual fertilizations. This will provide them with an immediate influx of nutrients. The damaged leaves won't heal but they shouldn't get any worse once the problems are fixed.
Yeah I would have to agree...I currently use Fox farm nutrients just started using it on my 3 month old clones