Thanks so much for the suggestions, guys.
Inflow is not the problem anymore. His fins were getting stuck, but I covered the part in the tank with pantyhose. Also used remembered conditioning.
He does have a plastic plant, but I didn't think much of it. I bought a silk feather plant to replace it with today, so definitely going to do that. Also got aquarium salt.
Question about the aquarium salt: should I take my fish out before I put the salt in, or is it okay if he's still in there?
I also spoke with the fish guy at PetsMart and he said it would be okay to take the filter out if there are issues. What are your thoughts on that?