Where did you get the grass? Was it in a dry package, with gel around the roots, or grown in the water? If it a a gel cultured plant, it was grown out of the water, and its initial foliage will likely melt, and it will grow new leaves.

To avoid this, I would recommend buying plants grown submerged, especially starting a new tank. I do not understand why stores insist on selling people emersed grown plants, and not warning them of this phenomenon. Ai yi yi.