When I first started out keeping fish, it took me awhile but I learned that if you have the animals best interest at heart, you’ll really consider upgrading the tank. Everyone starts somewhere there is no judgment for growth 🙂 what does his diet look like as well?
also quick tip. It doesn’t happen very often but I’ve heard that sometimes painted substrate can be harmful to fish. The paint can break down and decompose releasing epoxy a toxic chemical into the water leading to poisoning your fish. I believe he will get better with a tank upgrade and live plants instead of plastic. Plastic is always hit or miss usually not a good idea since it’s so sharp it’ll cut up your fish. It’d be like if we were in a very small cage with pins and needles sticking through a cage. We’d always get poked!!
however I do want to lastly say I’m proud of you. A lot of fish keepers will disregard the animal as worthless and just let it suffer. It’s incredibly admirable to decide to come to a whole new forum to educate one another as well and ensure that you are providing the best treatment for your fish!
blessings!!