You're only giving them a half bottle of water every four days? As in a 16oz. bottle of water? If so, 8oz. of water every four days is not near enough. Get a gallon jug and let it sit out a few days with the lid off to get the chlorine out of the water, and ensure your pH isn't too high or low. To check the soil's pH, simply check the pH of the water that ends up in the saucer.