Have you tested his tank for ammonia & nitrite? Red streaks or spots are cause for concern. You're doing what I do first, lots of water changes. Keep them up. They can work miracles! But if the red spots get larger, streaky or more of them, it may be time for an antibiotic. Salt can help with certain things but not most bacteria. Post another pic or 2 in a couple days.
& TY for the algae clump explanation, lol. But again, test!
As for the "finger shyness", try holding the tweezers down gradually closer to the food. He's new, you're both learning the "house rules". Fish & keepers learn by doing & hungry fish are often willing to try if you go slow. Try to wait a while before offering a 2nd bite & change up the foods. The food god(ess) should always decide what & when. He's made very good strides in only a few days. Reinforce that!