Java Fern needs to be attached to driftwood, rock or ornament. You can glue it onto them with superglue or tie it on with some white cotton sewing thread.
Anubias are garden plants that don't belong in aquariums. Lots of people have them but they aren't good for tanks. However, if you do have one, tie it to some driftwood or rocks like the Java Fern.
Guppy grass (Najas sp) should be planted in the substrate.
If you want floating plants look for Water Sprite (Ceratopteris thalictroides/ cornuta). It can grow on the surface but also planted in the substrate.
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I have never seen or used the Fluval substrate so can't comment. Others might have and hopefully they can shed some light on it.