need best way to lower salinity

Hi all! I just upgraded from a 29 gallon to a 80 gallon Nuvo a month ago...I have a refractometer.....checked my salinity and it was 1.029.....I usually keep it around 1.025.....now I have been taking out 1 gallon of water from the tank and replacing it with 1 gallon of RO water....I have done 3 gallons since last night but the salinity is only at 1.028......am I doing the right thing? How many more gallons? And how fast should I be doing this? Thanks for the help!