I fuse frog bit [ Limnobium Laevigatum ] , duck weed , salvinia , water lettuce [pistia] and water wisteria in many of my breeding tanks..
Fish love the protection from above. In nature if the predator is not in the water it comes from above and floaters really can calm some fish down.
Java moss can float along with some stem plants like hornwort or anacharis and anubias.