Quote Originally Posted by docwalker
Not if you maintain a proper pH. The reduction in alkalinity is a result of lower your pH to 6.8 or so which converts the carbonates into carbonic acid. Carbon dioxide is then released into the atmosphere by aerating.
I've been working on lowering the alkalinity from 220ppm to (now) 70-80ppm. I've -never- lowered the pH below 7.2 during the entire process. I have had to add acid when aerating, but that was my understanding of how it works.

But I see your larger point, that by not adding more acid, the pH -should- hold. When I hit 90-100ppm I was in a reverse situation because the pH kept bouncing back to 7.6. It looks like it's going to hold at 7.2 with the alkalinity at 70-80ppm. I suspect there's a chemical explanation occuring at the watersurface/atmosphere interface. But I'm not smart enough to explain it.