if u check out the leaf deficency chart ur answer shud b there, but it looks simply like lack of nitrogen, hence the leaf loosing its colour n goin yellow to brown to crispy, i am new to the game but have similar problem to u , and my research pointed to lack of feed especialy nitrogen as this is the key ingredient in keeping ur plant green, probly the hot weather did not help but still good lookin plant 2 me m8