Thanks everyone! I did not euthanize poor Astro. I kept him in a small separate tank and kept his water fresh and helped peel back his sheds off his legs (he couldn't remove them himself) until he passed. He was basically in hospice but without the drugs. I will look at the post about euthanization so I am better prepared in case I come into this situation again.
Thanks again. I hope Astro's short little life was at least sweet.