Check the carbonate hardness of your water. With pH swings like that, it must be soft. I have pH swings in my tank as well if I get lazy with water changes.
Maybe do a series of water changes to get your pH stable, then add a small amount of crushed coral and measure. Keep adding small amounts of crushed coral until the pH is stable. I wouldn't add a lot at once.
Maybe do a series of water changes to get your pH stable, then add a small amount of crushed coral and measure. Keep adding small amounts of crushed coral until the pH is stable. I wouldn't add a lot at once.
