I would say that buffering your top off is probably a good idea, imo
it never hurts. I use Kalkwasser for mine, but you could use baking soda. However, you'll want to do all the math. I.e. If i have a 5 gallon ato and I dose it with 4 tsp of baking soda, what will be the kh
, and ph, and what will that raise my tank by over the course of topping off. With doing water changes its important to match salinity, ph, and temp, bu with ato it shouldn't be that important. 1.) because true ro
will have neutral ph, and thus not effect your aquarium, 2.) if you are going to buffer your ato to keep up with alk
and calc requirements, then by nature there is very little chance it will match up with your tank parameters.