Ah yeah that long thing about ph... I read it somewhere too, can't remember where it's from...

It reaffirmed one bit of info I read about a few years ago, that high amounts of "free" CO2 lowers the water's ph. That's why totally plain water like distilled or RO doesn't have a neutral ph... because the CO2 in the air is absorbed into the water and there's nothing to buffer it, so it lowers ph.

Makes me think about how much ph can fluctuate on the first day after a res change... like for DWC, the ambient air already has a higher concentration of carbon dioxide than oxygen so when it gets pumped into the res. it all goes screwy. Aerating the water for a while before adding nutes and ph up/down solutions would sound like a good way to get it ready for a res change.

I've always loved the idea of hooking an oxygen generator up to the air tubes for the res, but I dunno the effects of higher concentrations of dissolved oxygen on water's ph.