Here is my short list for hard water fish... I already had them linked but I don't know if they transferred.(yep the links transferred fine)
I have water sitting at pH 7.8, 23dGh to start but it drops off to 17 after a week in the planted tank. Emerald catfish Bloodfin Tetra Black Widow Tetra Flame Tetra Pristella Tetra Cherry Barb
These are all community fish suitable for hard water and also aimed at around 2" fully grown sizing due to the numbers I wanted in a 37 gallon tank. The catfish are some of the few bottom feeders that are good at higher temperatures and hard water, they do get to 3.5". I was trying to match up with a male betta that I already had in the tank so these are about as non-aggressive as you can get.
I left out "show fish" or larger fish that are OK in smaller groups due to the betta, There area few gourami that can work I think.
If you just plow through the profiles here and skip right to the bottom first, that gives you the recommended tank minimum sizing, water hardness and pH and temperature ranges. The top gives you the temperament so it only takes about 10 seconds per fish, or less if they don't match one of the water parameters, to come up with your own short list.
I've been through the profiles often enough now I have gotten to know more about fish than I thought I would.