Join Date: Dec 2011
Location: Washington, USA
Sorry I'm a little late to this-- I love shrimp. :)
I'm crossing my fingers that it's not a disease-- if something mass killed the ghost shrimp, the resulting ammonia spike from the decomposing bodies could have been enough to stress out poor Lakitu. :/
Inverts in general are pretty sensitive to ammonia, and if you recently moved around a lot of gravel you could have stirred some stuff up (resulting in a minor spike). OR the plants had something that wasn't invert friendly on them. Sometimes copper is used in fertilizers. It shouldn't be enough to harm the shrimp, but it could have worked in combo? Anything metal is a no-go around my invert tank. I had a mass shrimp die-off years back because of a thin wire inside a silk plant rusting.
Anyway, I've kept ghost shrimp in freshwater for ages before-- and I doubt they were in brackish water in the store because it's harder to maintain and many people only use them for feeders.
You'll know more after you test the water, but keep in mind that if the ammonia is high it could be a result of the dead ghost shrimp (and not what killed them).