Danios: Zebras are tolerant of a wide range. Other species of Danios are more particular, generally prefering relatively soft water. GH under 9 degrees for sure, but check the actual species you have to see what they want.
Panda Garras are fine with a GH up to 12, they come from fairly soft water, but are adaptable. Fast flowing water is important.
Flower Shrimp thrive with a GH from 3-10 degrees.
GH under 3 degrees suggests there may not quite be enough Ca or Mg for the plants and livestock.
I would make the GH at least 3 German degrees of hardness, and up to 5 degrees is an easily achievable value. I do not see any need to go much higher, though.
I would also use potassium bicarbonate or sodium bicarbonate to get the KH to 3-5 degrees.