The copper might as well and have been the problem, all invertebrates are intolerant of copper, which is usually why they seem to suddenly die when ich medications are introduc into the tank as most contain copper. They can both survive with a small, diluted amount of copper as my fertilizer for the plants (seachem flourish) contains a very minimal amount of copper, my invertibrates don't seem to be effected in any noticeable amounts
While all invertebrates are intolerant of copper some do better than others, as you've found snails and shrimp are a good example. While shrimp would suddenly perish, snails might do a bit better off in the conditions.
There a even a few more examples in the home Aquarium, Plecos and Corydoras. While both are intolerant of salt as they are scaleless,Plecos tolerate it much better, and Corydoras almost die at a higher amount.
Yes, they would all die at once. At any sign of an unreasonable, unprefered amount of any substance will effect the live specimens within the tank negatively and can easily cause a mass death. Usually effecting the weaker first. Your other shrimp will most likely perish too unless the amount of copper is diluted
Last edited by Mo; 03-19-2012 at 08:14 PM.