All tds meters measure conductivity as a proxy for tds. Actual tds determination requires gravimetric measurement by evaporating H2O and weighing the residues, a tedious method not commonly used.
I’ve seen mixing different color Cherry shrimp nicely done, male only, so they won’t breed but need to be replenished regularly.
I don’t fancy my chances in obtaining single sex shrimps from on online supplier. I think my best bet is as you suggested - get a few Amanos and some Cherry’s and see how we go. If the Cherry’s breed, I can assume they are sufficiently comfortable and consider adding 4 of another species.
Assuming that happens, and given my water conditions of 225ppm tap water, CO2 injection so pH in the 6.0-6.5 region (tap water 7.0), temperature around 25 degrees C - what other shrimp species might be worth considering?