Newest Pickup, Couple of Questions.

I picked this guy up Friday for $80 which was a steal so I had to do it. He's probably 5-7" not 100% sure. But he hasn't eaten anything since I've got him, what can I do? The guy at my LFS told me not to worry it might take him a bit to get used to his new tank. Right now he is in a bare bottom 75G by himself. I will be getting sand for him once I figure out which color sand will make his colors pop better, and I will also add some driftwood and live plants. Is there something wrong with him or just him adjusting? Water parameters are, temp is 81*, PH 7.2, ammonia 0 ppm, nitrite 0ppm, and nitrate 5ppm. I tried feeding him, sinking carnivore, frzn bloodworms, frzn mysis shrimp, frzn beefheart, frzn krill, shrimp pellets and another frozen carnivore pellet and he hasnt eaten anything. Is my tank setup bothering him? I have a couple rocks in for him for now to hide in. I'm starting to get worried, I dont want to lose an $80 fish, especially when I see all the others go for $150. BTW he is a Teugelsi

Forgot pictures lol

Any other foods I should get him? Silversides or anything? Thank you btw I almost got him for ornate price but at the last second they figured out it was a teugelsi. Never saw one before and I love it. My LFS said its the only one that they've had in in over three years and only got it on a trade in.

Alright I'll try that. They were feeding krill at the LFS so thats why I tried that. Thank you!

What color sand is best for the dark bichirs? Im thinking about just going and getting play sand so I can start his tank setup