Is there a good natural non-fish-killing way to bring the alkalinity down?
acidifying pond
Peat, if you can carefully contain it and don't mind the water discoloration. It is often used in aquarium filters to lower ph. I have no actual experience doing this in a pond so please do some online research or defer to those who have. Try a prefilter when adding tap water to remove the minerals and salts responsible. This I do have experience with. Try www.pondbiz.com and search under chlorine control or water conditioning products. The System IV water filter does a modestly good job of keeping excess minerals out of tap water and a perfect job or removing chlorine. I wouldn't be without mine. I use it indoors for my 75 gal house aquarium and outside for a 400 gal pond and a 2000 gal pond. I havn't used dechlorinator for two years.
Thanks, snapple! I'll go to the link now.
50/50 water change with well water is the fastest and safest. Bellie