My Betta lays around a lot. When I first got him we was very weak from living in a cup. He got stronger but is still a lay about. Nitrates 20-40 really are not a big issue. My planted tanks run about that all the time.
Good clean water, vacuum, and do not overfeed and your boy should improve.
My Betta has the floating log and loves it more than the leaf.
I keep it out of the direct light too.