I agree with the others, these are the best.I'm assuming the thermometer pen and a liquid test kit for ammonia/nitrite/nitrate is best.
I'm not sure I understand, is the substrate from an already cycled aquarium? Cycling takes about a month without already cycled media/substrate.Nitrite/Nitrate is currently 0 ppm but ammonia didn't convert over yet I'm assuming, this tank has been running for 3 days now. I've been adding substrate to kick start that but waiting.
Your lower ph would probably eliminate danios.