I haven't added any Borax except in March at start up (to replace what was lost with partial drain/refill for the winter).

I do remember (from Gen. Chem. labs, faintly) that buffers reduce the swing of pH for a certain amount of acid/base added, and that they only have much effect within their useful buffering range, usually about 1 pH unit above and below the pKa. I guess what I'm not getting is why borate is of any use as at alL as a buffer at more than 2 pH units away from the pKa. I understand why the quantity of acid needed would be the same with or without the buffer--a buffer that is resisting a rise in pH also resists lowering pH back down.

My understanding is that buffers work by providing a "reservoir" of H3O+ through. If borate doesn't affect pH, then why the common advice here to use it to raise pH?

I'm really not trying to be argumentative, or put you on the spot--I just don't get it.

Chuck