Magnesium - Where Does it Go?

CastAway · Apr 30, 2014

I have a new tank, about a six weeks. At one point my Mg was over 1350, but now it's around 880ppm. I have no coral, no coralline. Calcium was around 450 at one point, and is now 395. Where does it go? How does a new tank, with no coral or coralline, metabolize Ca and Mg? Sorry is this is a stupid question.

ritter6788 · Apr 30, 2014

I would think that it's a testing error.

CastAway · Apr 30, 2014

Great. Ugh! I suspect he initial values were in error then, because they're pretty repeatable right now. I'm kinda cussing the Rea Sea tests. The color shifts are subtle, and don't match the cards. What test kit do you like for Ca and Mg?

Reefing Madness · Apr 30, 2014

I just use API for Cal.
Salifert for Mag.

Also, one cannot forget that Live Rock is dead coral, and will absorb some of those elements.

ritter6788 · Apr 30, 2014

Only 6 weeks, do you have any livestock in there? If not, I would just wait to test cal and mag when your cycle is good and done

CastAway · Apr 30, 2014

I have a damsel, two clowns and a blenny. There are five turbo snails, some ceriths, a couple hermits, and an emerald crab. Too much too soon?

ritter6788 · Apr 30, 2014

Hard to say for sure. Depends on if your cycle is done or not. When I used dry rock the cycle took a long time. Are you testing for ammonia and nitrites?

CastAway · Apr 30, 2014

They zero'd out some ago. Here's some history: https://www.reef2reef.com/forums/member-tanks/132276-jeffs-150-build-salt-box-11.html

Dalmatia · May 1, 2014

Magnesium is one of the most overlooked properties of your reefâ€™s synthetic seawater and although this is one of the most important factors considered in growth and health of most stony corals. Just like calcium and alkalinity magnesium is depleted by your reef inhabitants. It is also an important factor in maintaining stable calcium and alkalinity levels.
Just like all other ions in a reef tank you want to produce levels as close to natural seawater as possible. For this reason maintaining a level of at least 1290 to 1400ppm of magnesium is critical. Speaking from experience most stony corals will show lack of growth around 1100ppm and start declining in health at around 1000 or 900ppm.