[Bananableps]

Would it be possible for you to post bigger photos? Can't quite make out the detail of the leaves.

 

[Bananableps]

How recently did you add them? S. repens often takes awhile to get established. I still can't make things out very well in the photo, but it looks like the new growth is coming in OK. If the new growth is good, it's possible that the old leaves are in the process of shedding. This is normal. Commercial s. repens is usually grown in emergently, so it needs time to adapt to submerged conditions.