Your ammonia reading could be spurious, especially if using the API test kit.
That kit isn't good, frequently gives false positive readings. Suggest the Red Sea ammonia test kit instead.
Don't be overly aggressive trying to feed it while it's acclimating. It will just stress it.
Especially if it doesn't take the food immediately, and retracts instead.
Feed no more than once a week. Less often is fine as well.
I feed my BTAs small (3-5 mm) pieces of raw table shrimp (from the grocery store.)
A good rule of thumb is to only feed pieces of food smaller than the anemone's mouth.
I feed it to them with a plastic pipette with cut off end.
This lets them get the food, and keeps fish from stealing it first.
Don't use a metal tweezers/forceps to feed nems; they don't like the feel of metal.
Don't do carbon dosing with vinegar or alcohol unless you have a specific need to do so (nutrients too high.)