My cherry shimp do very well in 7.0-7.2 pH water. The CRS (crystal red shrimp) do like softer water which is why I have a hard time keeping them. I have oyster shells with moss growing on them in my tanks but there is no change in any of my parameters, so it probably doesn't matter. You want to make sure the tannins leach out first before you put the driftwood in the tank. It also helps to keep the wood sunk into the water and not floating. Tannins will change the water parameters and I don't what it will do to the shrimp, but I wouldn't want to try it and find them all dead the next day.