Save my tank!

[asylumdown]

I think you have to do what I did when I didn't know what was happening to my tank - stop absolutely everything that you're doing/dosing, and start a campaign of massive daily water changes. Change that water as fast as you can make it, up to and including at least 1 100% water change. Do this with a better salt than IO, something that mixes up with alkalinity closer to NSW levels.

Something is wrong in your tank, and by extension your water. You can bang your head against the wall trying to figure out what, but sometimes a 100% reset of the medium your corals are immersed in is the only way to completely eliminate all the unknowns.

I'd continue doing 20-40% daily water changes until the surviving corals stopped declining and started to improve, then I'd switch to once a week water changes, but bring the doser back online and adjust it every day as needed after testing alk, calcium and magnesium. I'd only switch to once a week testing after things definitively stabilized.

This saved my tank when I couldn't figure out what was killing my corals, and it saved it again after my tank nearly died during a renovation.