cym leaf tips turning brown?

[kindrag23]

This is my new NOID Cym I got from home depot. I repotted it due to it being in a pot that it had broken out of. I did not feed it when I first got it bc I noticed the miracle gro mix I could find in town (only thing there was to find) said it had food in it. I sprinkled a small amount of osmocote slow release food on top of the media for food as well in case miracle grow is not enough. I noticed when I first got it that the leaves seemed to be covered in salt build up so I flushed it as much as possible after repotting it. Its roots are full and thick and barely fit in my 2 gallon gardening pot I got for it....it had a few tips that were turning brown. Now there are more and they are really brown!

My other Cym same space quite happy. The browning leaves.....could this be Sun burn? They were in the middle of my home depot w no access to light...so maybe it Is scorching them? We will have another day of 80* weather then this weekend snow and ice....