Is it possible that the crypts are using up the nutrients in the water, but having a big root system, can continue to grow from root feeding? That would leave the newly planted vals and microswords short of nutrients, but without the roots needed to feed that way.

Also, I have always had problems getting vals to start growing when first planted. They almost always shed all of their leaves, leaving only a rooted stub. Eventually that stub sends out new leaves and the vals become the nuisance they can become. Since I have never had E. tennellus grow for me I can't comment on that.