Co2 definately has a bearing on ph and with lower c02 goes higher ph. As for macro algae, it will indeed consume trace but perhaps a different way to dose it would be in order. Yet, with a good regiment of wc it should be fine. Do you icp to have an idea on trace consumption? Is it an icp-ms? Here's my ph after I left for vacation on Saturday i.e. 3 less humans and 2 less dogs in the house. I use soda ash but have been lucky with higher ph as where my tank is happens to be a big open living space and probe is calibrated. For now, if you do a 10-15% waterchange every week and a half or so your salt should provide everything needed for what you have. My tank is acro heavy and that worked for me for a long time.
