Hi Wendy
Welcome to SimplyDiscus. Nice to see another NW person. Sorry you're having problems. It is not unusual for new arrivals to take time to acclimate to their new environment. Some may eat right away, others may take several days or a week, so that alone is not a problem yet. What you describe on the fins and the scraping could be some minor ammonia irritation from the shipping. Keep up with the daily water changes and it may go away on its own. Most folks here don't place much value on Melafix. Keeping up with water changes is the usual recommendation. The white poo is more troubling and could suggest an internal bug as you suggest, but again, before medicating, I would see how they react after a few days of water changes. I'm not a medication expert, but if the problem continues, you'll get advice for a common medication (Metro). I would encourage you to contact the supplier and see what they suggest also.