I think you have done everything possible! Let's just hope he come through, (it sounds like he might). I always check the water quality from the store, I take my syringe and fill up a few glass tubes and check
ammonia, NitrItes, NitrAtes, Phosphates,
pH and I even have a conductivity meter that I stick into the fish tanks when I'm at the store! It usually freaks out the employees!
"Conductivity" is an issue that most hobbyists do not even consider, (I'm just learning about it myself). I'm finding out that most of the water in LFS has a conductivity level of 1500-3000, and our tap water is around 300-400. I found out the hard way because I use
RO water which drops my conductivity to 150. This creates a pressure difference between the fish gills and the outside water pressure, it has a similar effect for deep sea divers called “the bends”.
This web site has a great article from Joe Gargas. I highly recommend everyone in the hobby to read it. Pay special attention to the trips to Wal-mart.
http://www.tbas1.com/TBASpdf/May2009.pdf