Calathea Warscewiczii HELP!!!

A little history. I have had this about two months. Until about two weeks ago it was growing and healthy. First problem was that the leaves began to get hard dry edges. I did some research and found many answers that it needs more water. Until this time I had only watered on Saturday. I began adding a top off of water on Wednesdays not a full watering just some on top. The problem then became yellowing leaves too. I took it out of the east facing bay window and put it on the coffee table near the east facing bay window. Problem grew worse so I brought it to a garden center and they suggested I add a miracle-grow type feeder. Now its even worse. I am slowly killing this beautiful plant with love and good intentions. I know have moved back into the bay window and have started spritzing the leaves with water too. HELP before this beauty dies!!!!

 

I don't think it looks so bad. Old leaves die. They are supposed to do that. Cut them off. That will happen on the plant next to it too.
I don't know about the curled leaves - it's probably something, or are they new leaves unfurling?
Try to figure out the watering. You can't go by days of the week. Water it thoroughly, make sure it is nice and heavy, and remove any water in the tray (there is a hole in that pot, right?). Feel how heavy that is. See where the leaves are then in the daytime. When it feels definitely lighter and it's dry on top and the leaves start to droop, then it's time to water it again. No top-offs - just water it completely when it needs water. You want the roots down at the bottom, so don't just give them a little water at the top.

Had it just been repotted when you got it, or did you repot it? If not, you could take it out of the pot and make sure it is not pot-bound and in need of repotting. And smell the soil too, see if it smells ok (and not smelling as if roots have been rotting).

Maybe someone else can speak to the light requirements. I have a Calathea in an east-facing window next to a 6' deep balcony overhang. I don't think they need good light.
I would make sure it's ok before fertilizing it again, and make sure you only use half the recommended amount of fertilizer, and maybe only every other time you water it.