Agreed, you shouldn't have to be dosing mag on a regular basis..... very little mag is utilized by corals, it's presence is more to prevent the alk
& calc from precipitating out of solution.
If you only have 3 small colonies of SPS
in an 80g tank, you really shouldn't need to be dosing at all......... regular pwc
's should be providing those with what they need.
And, from experience, you don't need to keep your calc & alk
that high, either. You'd think that keeping them at max levels will provide your corals with more food, but it just creates other problems...... I use to keep my alk
right at 12dKh, and I didn't get any faster growth out of my corals, but my pumps & heaters certainly built up calcification much
quicker. 400-420 calc & 8-10 dKh
is plenty to supply your corals with what they need.