Try addition of a drop of ammonia (rather diluted) and leave your vessel after cooling to RT for a month or more.
Upon making a saturated solution, it almost immediately forms a thin layer of crystals on the surface of the solution. These crystals are good enough for me. The only problem is that only these desirable crystals only grow on the surface. On the bottom and along the sides, there is a different type of crystal growth. I have two questions.
1) Why do the surface crystals grow differently than the others?
2) What can I do to force all of the crystals to grow the same way that the surface crystals grow?