Going back to your original question, rinsing/washing the aragonite will only remove dust. It will not change its buffering capacity. Meaning, if it releases substances to raise pH and hardness then rinsing wonít change this.
Iím in a similar boat regarding substrate. I have a 20g with a very fine layer of black sand (tons of mosses) and a 6.6g with no substrate. RCS in the 20 and yellow neos in the 6.6g. Shrimp are feeding and breeding decently in both tanks, however, Iíve been advised that fry yield would increase with the addition of substrate (the idea is that there would be more surface area for biofilm). With neos I could probably get away with an inert substrate or an active shrimp specific substrate (one that lowers pH, GH
, and KH
). Itís just that the bare bottom tank is so much cleaner.