I think it 9dkh you could stand to drop your Ca to around 420-5 range, as your tank is dropping so much and see if that closes that gap a bit. Also lower Mg to1350-1400 range.
I never liked keeping Alk real high recipe for disaster not that 9 is real high but better to lower your CA then push your ALK IMHO/E
Is you tank heavily stocked?
Yes. Tank is heavily stocked. I have around 40 heads of candy cane, one pagoda coral that is around 5-6" in diameter, a pipe organ that is a little bigger than a baseball and growing fast and the two clams that are over 5" now.
Besides that I have finger leather, 3 kinds, kenya tree, dinner plate size toadstool, 4 kinds of mushroom, gsp, 2 types of xenia and a few polyps. Rocks are covered in coraline. Even my drain hose has coraline inside where the light hits.
I havent been adding magnesium, it is just high.
I do a 5 gallon water change every week, so fhat is a little over 10%.
I dont dose anything else besides the Cal and ALK.
My levs drop if I dont dose, but the two part keeps them constant. My issue are the PH spikes from adding the ALK. That is why I wanted to try baking soda, and since I saw that mixing baked and unbaked soda will keep PH around 8.2-3 I thought it woukd be perfect.
Also, thanks everykne for the help and links.