is my inherited black moor okay?

I have a beautiful black moor that I love a lot named Sharkey (like a hammerhead shark!) who I recently inherited from my parents. My parents were fine keeping him (not sure his gender or age, would love to know!) in this tiny 3 gallon. I intervened and placed him in 20 gallon with a filter, where he lives with a calico fantail that hangs out with him a lot.

I detected an ammonia spike recently and did a 50 percent water change. I’m worried that he’s getting orange unnaturally, may be too skinny (my parents are weird and say you should feed growing goldfish every other day, and their most ridiculous claim is that you can go without feeding them for a month, or his fins are unhealthy.) I don’t know if I’m being neurotic of if there’s something wrong.

He moves pretty quickly but sometimes stays still after he eats. He seems very active and I don’t think I’ve seen the other fish, Orange, nip his fins. I have seen orange get foodies faster and eat it up so I’m worried that Sharkey is undernourished.)

(I do water changes when I can but my parents are grouchy about me spending so much time on a fish (which is ridiculous.) I am moving away soon and I can’t stand the thought of leaving my fish with people who don’t care about them. I am considering giving Sharkey and his calico fantail friend, Orange, to a specialty fish store with spacious good tanks where I hope they can care for him well and give him to a more responsible owner.

Owning fish is terrifying and I get scared and cry a lot every time fish gets sick and/or dies. I love my fish a lot and hope nothing happens to them.)

Attached are some pictures. I put him in a small cup while changing the water and fed him so he can get the food without Orange stealing it, and then promptly put him back in the tank.

I'm sorry no one responded to you! Update please? If he's still alive, I'll @ some people who I think can help

He is alive.

Unfortunately I gave both Sharkey (the black moor) and Orange to a local small fish store that takes very good of its fish. Because I'm a beginner I don't want either of them to suffer in my hands.

For my own future knowledge, I'd like to know if anything looked wrong with Sharkey.

Before I gave them away I did a 50% water change with Seachem Prime and Stability when the tank looked cloudy and 3-4 days later, it was cloudy again. I tested the water and got 0.25 ammonia and 0 nitrates. The pH also dropped to 6.2 and I don't know why.