What color was the bta when you got it?
Feeding it everyday stresses out anemones as it takes more energy for them to digest the food than they actually get out of it. Some people feed them regularly to force them to split, but it's just splitting becuase it's stressed and trying to survive.
You saw a white chunk floating around? If possible get it out of the tank. If it happened to be your bta dying (they dissolve when they die) it will likely kill everything in your tank.
If the bta is still alive give it like 1-2 hours of light a day for a week or two then add about an hour every 10 days. It's a slow but safe way.
If the lfs
was keeping them in regular flourescent and feeding them daily then I definitely wouldnt believe anything they told me.
If by chance the bta was white when you got it, you must feed it for several weeks to nurse it back to health then maybe feed it once a month. They get all they need from the light and water column.
And you should of drip acclimated it for about 3 hours.