I don't know the specifics but you could start at 5.0 pH, 80 degress and less than 1 degrees(may not need to be this soft) hardness, lots of clean blackworms and mosquito larve. Don't change the water for two weeks and then do a 50 percent with cool water (70 degrees). Then stand back.
If you don't have access to rainwater, I used to use distilled water. This is practical (sort of ) if you are working with one species at a time.
BTW, are you sure you have viejta?