Syno cats don't like big water changes, they are very sensitive to PH changes and chlorine...Did you add any PRIME to your new water?
If you have seachem Prime on hand add some now but you're really going to have to wait and see, Another big help would be if you can acquire some, add some seachem Stabilty.... He may just pull through.
These are two great products to use with your wc's, I always use the prime with new fresh water (from the tap) and keep the Stability on hand incase you have a freak crash....
http://www.seachem.com/Products/prod...ges/Prime.html
http://www.seachem.com/Products/prod...Stability.html