+1 on the alk. What is your alk reading? How and when are you dosing alk? Dosing in the evening or throughout the night may help some (depending on how you supplement).

Another though... reverse light cycle on a fuge with chaeto and/or other macroalgae may help.

Off the wall idea... house plants? They would suck up the CO2 during the day.

BeakerBob's expertise may be helpful... perhaps this thread could be moved to his Discussion with the Experts section?