I have a tap water with high pH (approx. 8.0) and high carbonate hardness (180ppm) and currently keep a variety of Corys, plecos and geophagus. In a few weeks, these fish will move to a new set up with pH= 7.0 and Carbonate hardness of around 40-50). What methods would you suggest to make the transition and over what period of time would you do it?