A possibility is the water quality. With chlorine treated tap water letting it sit out for 24 hours will evaporate the chlorine. BUT many local reservoirs are treated with chloramine which is a blend of ammonia and chlorine. What the ammonia does is keep the chlorine from evaporating, therefore the city spend less money keeping the water treated because the chloramine will not evaporate. How it affects the plants is that the chlorine is never removed. Im not aying that chlorine is the exact culprit because sodium, flouride, and many other additives will not evaporate either, and those a like poision to plants. I would suggest trying a product like flora kleen or clearex along with reverse osmosis or bottled water. When using bottled water be sure to check the label to make sure it does not contain sodium. Crystal gyser is good, and arrowhead is good also and contains about 250ppm of natural minerals. Try 2 normal waterings with the above suggestions, than go back to a normal feeding schedule. A visit to your local water companies website should have all the things they add to the water listed, and you can go from there. Good Luck and I hope this was helpful in some way.