... I tested the alkalinity of my effluent and it’s at 20.0 dKH which @Jose Esteves recommended.
I know that is the target some use. Some use 25 dKh. BUT... 20 dKh may be way too high for your very low demand system even at 1ml/min of effluent flow. I would target the alkalinity in the display tank rather than the alkalinity of the effluent. Let's say you want display tank alkalinity to stay stable @ 7.5 dKh. Once you set it there, (USE BAKING SODA TO RAISE ALK) you only need to replace what is used. You may find that you only need a little added alk to meet your demand right now. An effluent with a dKH of 8 or 9 might do the trick. It will take more when demand increases as you add growing hard corals and Coralline algae starts growing. Don't get distracted by theoretical numbers. I would start at 1 ml effluent flow, and a pH several tenths above what the media manufacturer recommends then start dialing in from there.