I use RO water and add some seachem equilibrium to it to keep up the hardness (hopefully more than just GH). the resulting water in the tank is very soft.
if the tank needs to be topped off, I top off with pure RO water
Water changes are now 80%. I have started to leave more water in to reduce stress on the shrimp during the water change.
If you notice something wrong with the water i am preparing/using, please let me know!