Whether you using RO or RO/DI you will need to remineralize. RO will just require a tiny bit less of remineralization. You do it based on the target GH you want. Then you just use ferts like normal.
Although honestly if you don't need a very specific GH for finicky shrimp I wouldn't bother and use regular tap for the water change and keep ro/di water just for ato purposes. Using 0 tds water on the ATO will keep the TDS from spiking as water evaporates.
My RO/DI creation is fully automated. I can give you a quick rundown on what's needed if you want to try that route.