Fish, shrimp and other aquatic organism are regularly subjected to massive water changes in the wild when it rains. If you have shrimp in the aquarium that die simply because you do a 50% water change, there is either something in the water you are adding or the shrimp are poor quality, inbred, genetically weak.
As long as the new water going into the tank is free of chlorine/ chloramine and has a similar temperature & chemistry to the tank water, there should be no reason why fish or shrimp should have an issue with a 90% water change.
When you get new shrimp, do you put them in a bucket with the water they came in, and slowly drip tank water into the bucket until it they are in 100% tank water? Or do you float the bag in the tank and add some tank water, wait 15minutes before tipping the contents into the tank?
My guess is the latter.
As long as the new water going into the tank is free of chlorine/ chloramine and has a similar temperature & chemistry to the tank water, there should be no reason why fish or shrimp should have an issue with a 90% water change.
When you get new shrimp, do you put them in a bucket with the water they came in, and slowly drip tank water into the bucket until it they are in 100% tank water? Or do you float the bag in the tank and add some tank water, wait 15minutes before tipping the contents into the tank?
My guess is the latter.