I filled my tank wednesday and noticed a severe drop in pH. The water from the tap is ~7.66, and after about 18 hours in my tank the pH had dropped to ~5.55! After 2 water changes, my pH rose to ~6.72; I started CO2 injection yesterday, a little bit higher than 1 bps. Went to sleep, woke up and my CO2 levels are perfect (according to the drop checker), and my pH has only gone down to around 5.84. I'm going to set my pH controller to inject maintain this pH (5.85), do another water change, and see what happens. I'm curious to see how low the pH will settle.
Do you have a drop checker?