OK,

You're getting good advice, but there's a catch: The aeration doesn't lower your Alk, it raises pH without raising Alk.

Alk tags along with pH normally. You lower your pH, Alk comes down with it. pH goes up, normally Alk does too.

So you lower your pH to 7.0-7.2. Then measure your Total Alkalinity (so you know where you are). Then you aerate to raise pH without Alk going up. If Alk is OK, you are done. If still high, you lower pH again, dragging down Alk with it, and aerate to raise it.

It's a little confusing to say that Borax doesn't raise Alk and that it does. But both are true. When Borax raises pH, Alk will rise correspondingly. This is different than Soda Ash (Bal Pak 200, or pH Up) which will not only raise pH, but will increase the Alk even more so. So if you raise your pH with Soda Ash to, say, 7.8, your Alk will go up a good bit more than if you raise it with Borax.

But aeration (for reasons I barely understand and cannot explain) raises the pH without raising the Alk at all.

Hope this helps....