Flanders "“ I'm not buffering at all. I have no calcifying corals and I would have thought that 5% water changes every week would have been enough to keep the alk up. I also have an aragonite sand bed of about 3"; wouldn't that contribute to the buffering capacity as well?
IMO, you should be buffering. alkalinity will gradually drop in all marine aquariums over time. water changes are helpful, but unless the new water has alkalinity elevated above NSW levels, or they are very large, they cannot be expected to restore your alkalinity without additional buffering.