Burning through magnesium

[mrbacony]

My alkalinity is around 8.3 and calcium at 400. I have to dose both every 4-5 days to keep levels up. But my magnesium drops very fast. I tested 2 days ago and it was 1350. Today it was 1200. This seems to happen a lot. If I go more than a day or so dosing magnesium, it will drop like 100-150 ppm. Any reason for this?
I only have one small favia, a 2 headed hammer, 4 small zoas and a rhodactis.

 

[Nano sapiens]

Coralline algae are known to uptake a good amount of magnesium when growing.

 

[SPR1968]

Are you using a Red Sea test kit by any chance?

 

[mrbacony]

My tank is newly growing a lot of coraline currently.

I use Aquaforest test kit

 

[Spare time]

I doubt its the coraline. I use about 100ppm a month in my 75g covered in coralline algae.

 

[Robinson]

I suggest checking your test kit, I had a similar experience and was dosing constantly to try to keep up with the apparent consumption. Finally decided to do a ICP test and magnesium was around 1600 when my test kit was giving me 1250 and dropping. Started to notice that some inverts were dying. I got another test kit and that one confirmed my ICP results. The original test kit was not expired but wasn’t giving accurate results.

 

[Spare time]

I suggest checking your test kit, I had a similar experience and was dosing constantly to try to keep up with the apparent consumption. Finally decided to do a ICP test and magnesium was around 1600 when my test kit was giving me 1250 and dropping. Started to notice that some inverts were dying. I got another test kit and that one confirmed my ICP results. The original test kit was not expired but wasn’t giving accurate results.

Which kit?

 

[mrbacony]

I used the reference solution that comes with the aquaforest test kit and it was right on. So I don’t think the test kit is off.

 

[X-37B]

Get a salifert test kit and recheck.
Mag does not get used up at that rate. Something is off.
Take a sample to your lfs for a quick check.
How big is your tank?
For stability you should dose alk and cal daily.

 

[Randy Holmes-Farley Verified Community Expert]

My alkalinity is around 8.3 and calcium at 400. I have to dose both every 4-5 days to keep levels up. But my magnesium drops very fast. I tested 2 days ago and it was 1350. Today it was 1200. This seems to happen a lot. If I go more than a day or so dosing magnesium, it will drop like 100-150 ppm. Any reason for this?
I only have one small favia, a 2 headed hammer, 4 small zoas and a rhodactis.

That drop cannot be anything except test error or a large salinity drop. Magnesium is not consumed more than about 2 ppm per day, and would typically drop about 1/10th of the calcium drop,

 

[Randy Holmes-Farley Verified Community Expert]

I used the reference solution that comes with the aquaforest test kit and it was right on. So I don’t think the test kit is off.

In any case, consumption did not cause a drop anywhere close to what you reported.

 

[Robinson]

Which kit?

Salifert

 

[mrbacony]

I will pick up a Salifert or other kit and try it.

 

[wilsonline]

Did you find the issue?
I'm talking to a buddy here that has the same issue. I can;t see any other possibility other than test error, low salinity, or wrong math on the dose. I don;t know a reason for that to precipitate nor to be the uptake (lol).

 

[aurora.k]

Mag does not get used up at that rate. Something is off.

I agree with this. I have basically never dosed mag with regular water changes but have to dose Kh and calcium daily

 

[mrbacony]

Pretty sure it was my test kit. I am now using Salifert and it stays fairly steady. I still have to dose but it is not as dramatic a change.