I'm experiencing high alkalinity (Alk) consumption in my tank for no apparent reason. I performed a water change on Sunday, as usual, and tested the alkalinity today to check, finding it at 7.4 dKH. Out of curiosity, I mixed a fresh batch of 4 gallons of saltwater, which is my typical weekly water change volume, using my usual salt, Red Sea Coral Pro, and let it mix as instructed. The fresh batch tested at 12.1 and 12.2 dKH across two tests.
I have four small coral frags but a significant amount of coralline algae. Is it possible that the coralline algae is consuming that much alkalinity in about a week's time?