Why do my numbers fluctuate so much?

[ZaneTer]

Some of the numbers the op posted are definitely error. Magnesium drops less than 2 ppm per day, assuming salinity is constant. Never more. The calcium dropping 400 to 260 is also error.

Hi Randy, please would you explain where the 2ppm magnesium drop comes from?
I am away from my tank for 3 months and I would like to know roughly when I should dose 50ppm magnesium. Is there a calculation I should follow to predict when?
Thanks

 

[Randy Holmes-Farley Verified Community Expert]

Hi Randy, please would you explain where the 2ppm magnesium drop comes from?
I am away from my tank for 3 months and I would like to know roughly when I should dose 50ppm magnesium. Is there a calculation I should follow to predict when?
Thanks

If you are not measuring magnesium, it can be hard to know. 2 ppm is a max rate, not a typical rate.

it comes from understanding what ends of in calcium carbonate that is precipitated (the only big sink for calcium and magnesium).

For each 1 meq/L (2.8 dKH) of alk consumed by calcification, about 17.5 mg/L calcium and 1.5 mg/L magnesium is consumed. THus, unless you have more than 3 dKH of alk consumed by calcification each day, you are unlikely to have even 2 mg/L (2 ppm)of magnesium consumed.


I discuss that in detail in this question of the day:

Reef Chemistry Question of the Day #200 Calcification and The Big Three Parameters

Reef Chemistry Question of the Day #200 Natural seawater has roughly the following parameters at 35 ppt: 420 mg/L calcium 7 dKH (2.5 meq/L) alkalinity 1280 mg/L magnesium. Let's imagine a typical coral reef aquarium with a mixture of different types of hard corals and coralline algae. Which...

www.reef2reef.com

 

[ZaneTer]

If you are not measuring magnesium, it can be hard to know. 2 ppm is a max rate, not a typical rate.

it comes from understanding what ends of in calcium carbonate that is precipitated (the only big sink for calcium and magnesium).

For each 1 meq/L (2.8 dKH) of alk consumed by calcification, about 17.5 mg/L calcium and 1.5 mg/L magnesium is consumed. THus, unless you have more than 3 dKH of alk consumed by calcification each day, you are unlikely to have even 2 mg/L (2 ppm)of magnesium consumed.


I discuss that in detail in this question of the day:

Reef Chemistry Question of the Day #200 Calcification and The Big Three Parameters

Reef Chemistry Question of the Day #200 Natural seawater has roughly the following parameters at 35 ppt: 420 mg/L calcium 7 dKH (2.5 meq/L) alkalinity 1280 mg/L magnesium. Let's imagine a typical coral reef aquarium with a mixture of different types of hard corals and coralline algae. Which...

www.reef2reef.com

Thank you so much for the detailed and explanatory reply. It is very appreciated.

 

[aquaman99]

Some of the numbers the op posted are definitely error. Magnesium drops less than 2 ppm per day, assuming salinity is constant. Never more. The calcium dropping 400 to 260 is also error.

I have had my numbers stable since my last post on here. CA 420, MG 1350, and KH 8.5. But ai just got another CA of 260. It has to be an error like you said but I’m not sure what I’m doing wrong to get 260 multiple times in a few weeks span?

 

[themcnertney]

I say let them fluctuate. As long as they consistently fluctuate day to day, all should be well. Its those really crazy shifts that will be headaches.

 

[Randy Holmes-Farley Verified Community Expert]

I have had my numbers stable since my last post on here. CA 420, MG 1350, and KH 8.5. But ai just got another CA of 260. It has to be an error like you said but I’m not sure what I’m doing wrong to get 260 multiple times in a few weeks span?

I can't know either, but some test issue.