Sorry for the dealy in responding! These plants are suffering from nutrient deficiency. This could be the result of too much or not enough water. Roots suffering from rot or dryness cannot function sufficiently to carry nutrients into the plant, even if fertilizers are added. Check with your local garden center or agricultural supply store (which may be the better option for this) for an appropriate fertilizer. Keep in mind, we typically see browning of leave edges (margins) in response to under-watering, and/or nutrient excess. Water should be applied when needed (according to weather conditions and plant size) rather than on a fixed schedule. Water deeply fewer times per week as opposed to daily, and maintain even soil moisture (avoid fluctuations in very dry and very wet/flooding of soil). Also, not applying enough water along with fertilizer applications causes the mineral salts to build-up in the soil around the roots, causing root damage and “leaf tip” or “leaf margin” burning.