I was of the understanding that adding peat to filtration lowers pH by adding humic acids to the water. But does it actually do ion exchange to lower KH or GH?

Also does adding co2 actually decrease the KH (as many sites claim)?

I was under the impression that it softened the water as well as lowered the PH.

Not sure about your second question. Sorry.

CO2 doesn't lower the KH, but it does change the pH. My understanding is that peat lowers the KH by some kind of ion exchange. I think I recall someone explaining that here.

I have a similar question.

Absent CO2 injection, my understanding is that all other things being equal, water holds more CO2 at a lower KH, thus the pH falls as the KH is lowered.

Is this correct?

Bill

Further to my original post...I looked up some info and it appears that peat CAN possibly do ion exchange to reduce Ca and Mg by releasing H+ (assuming it isn't already saturated with some other heavy metal). No mention of carbonates though, so for now unless I test it or hear otherwise I must assume that it only effectively reduces GH. But it does release humic acids which would lower pH, presumably.