LeslyHi Misty,
I have a 23 month old daughter who is small......22 pounds. Sounds like your son is TINY at 27 pounds. My daughter is SVCAH, so I can’t answer your question as far as salt wasting goes, but I do know it is common to have weight issues with CAH.
My opinion would be to make sure his levels are at optimal level with so many risk involved with him.
Good luck,
Lesly