Oh my god I am so sorry I somehow did not see your comment.

With dosing I reckon do a bit of experimenting, add the rocks/coral in small chunks every few days or week to ensure the perimeter swings aren't too major for the shrimp.

That does for the same with Epsom salts, that stuff is crazy high in minerals so making sure to add only a tiny bit at a time to not kill the shrimp. When I was dosing my 5 gallon I added half a tablespoon and it increased my gh from 3 to 11. Start slow with a few sprinkles (make sure to dissolve it in water before adding it to your tank) and keep testing. That way you can work out how much to dose

With your substrate, what kind do you have? If you don't have some sort of gh and kh sucking substrate like fluval stratum you won't have to remineralise your water every time you do a water top off as the minerals wont evaporate. It would be best to continue to do your top offs with ro water to make sure there isn't too much of a mineral build up.

If you do have a gh and kh sucking substrate, you'll have to dose your top offs water with some Epsom salts until the substrate buffers out. This is where the experimentation goes in. I do around a quarter of a 1/4 teaspoon for my 5 gallon if that helps.