[Randy Holmes-Farley]

It is certainly true that the low pH that comes from CO2 in shipping bags may help animals deal with the ammonia that is building up. It has been speculated that if you raise the pH by mixing in tank water, that ammonia may be a concern. Toward this end, folks believing this tend to focus on longer transit times. The longer the fish has been in the bag the worse the problem is likely to be.

I think a practical approach is best. If the fish has been in the bag just from the LFS, ammonia is not likely a concern. After a day, or worse, two or more, ammonia may be a big problem, and more care may be necessary.

One way around this is to find out in advance what the salinity of the water is that the fish is coming in, and then set up a temporary tank or container at that salinity. maybe even cooled a bit as the fish will likely arrive cooler than normal. Then you could move it much faster from the bag to a safer system.