Browning on leaves

calclium deficiency -- pH too low (way more often than high), nute lockout or simply too little Ca provided.... The first two often cause coinciding symptoms of other 'stuff,' so i'd go with low Ca levels as the cause in this case. It's 1 symptom and matches well. Leaf symptoms are not discrete, meaning more than 1 cause is possible and requires a process of elimination using more information when possible.