Yellow leaves are the result of too much light or fertilizer. Sticky substances are usually the result of insects. Cleaning the stalks and changing the water is also a good practice in these cases. When you say the stalks are wobbly and soft, I assume this is from the bottom up. If this is the case then over-fertilization has probably occurred and cause unrepairable damage. My suggestion would be to cut off the stalks above the soft wabbly section and root the tops. Clean your container and fill with distilled water before you place the tops back in the container. I would use a rooting hormone on the cut.