Well, I guess I will put my 2 cents worth in too. Where I keep my Ro water the temperature is only around 72F. but the fish room is 79F. So what I do is add 120F water from my hot water tank until it reaches the desired temperature. I have been doing this for about 10 years now and depending on how new the RO unit is and how much hot tap water is needed, I end up with a TDS reading of about 34 ppm which works well for me. My tap water starts at 175ppm with a 7.5pH. I have a pH meter somewhere but don't use it very much as I don't like trying to change it as it still fluctuates so much anyway. I do end up with a 6.0pH most of the time (when I check). Now I know there are many ideas on how to change water conditions and I figure whatever works for each person is correct.
Don