Problems Growing an Arrowhead Philodendron?

I have always had an arrowhead philodendron in among the houseplants I keep. They have always thrived, been bushy and long in the stem. I usually keep them in spots with good filtered light or direct light, saturate the soil, then allow the soil to dry out.... and the plants have loved it. Now, however, I have one that was rescued from a single living leaf, grew to have 3 leaves, and is dying off again. I follow the same principles, and they don't work. All my other plants have soil from the same bag, so I'm not sure it's that. There is a single tiny sprout at the base of the stem, and it would appear to be growing (painfully slowly). It's about half a millimeter in height and has been that way for weeks. I tried moving the plant, tilling the soil, using fertilizer, take-root powder...nothing is working. Any thoughts?