BTW...I tried all the more simple things first like adding airstones in my sump. More costly things like more effective water movement in my tank by adding 4 Ecotech MPs. Both moves were good and remain in place, but didn't solve the sustained low pH. It wasn't until I started reading here and elsewhere about this issue with newer homes that I tried opening a slider and window during the summer (obviously not practical on hot or cold days) did I narrow down the source of the problem, co2. I considered both the in-line air filter and outside supply, even had my itchy finger on the purchase button for the filter and then decided to give the outside airline a try. I will see this winter if I have any cold temp issues, but went through some sweltering hot periods with no heat issues thus far, and that is usually a bigger problem with most people's reef tanks. I've read that some people in colder climates put pipe insulation around d the first few feet of the intake coming in the house to reduce the possibility of condensation freezing.
