Mg impact on SG and Ca

Just throwing up some numbers from my log as my Mg recently dropped.

I only dosed Mg in this time frame (other than my auto dosing)

4/18: Mg: 1460 sg: 1.027 Ca: 430
5/12: Mg: 1500 sg: 1.027 Ca: 430
6/06: Mg: 1335 sg: 1.026 Ca: 360
6/11: Mg: 1410 sg: 1.0265* Ca: 400
6/13: Mg: 1480 sg: 1.027 Ca: 450

* I pay attention if the refractometer is on the upper or lower part of the line and log as such


You can see 40ppm of Mg didn't really make an impact.

165ppm sure did. A full sg point and about 100 points of Ca.

75ppm and 70ppm difference (negligible) did a 1/2 point of sg and 50ppm of Ca.


I'm sure there's a margin of error in there, so this is just for reference.

 

awesome... my Ca is usually around or above 520mg/L so that must mean my Mg is high too. SG is around 1.021, I use H2Ocean Salt

 

Even as just a reference it's very useful info! Thanks for sharing.

 

You have my thanks as well K+

 

Thanks

 

I highly doubt at such a low salinity that a CA of 520 that your MG would be to high, common sense dictates it would be lower

 

Interesting to see an example of this happening. It may not be just the Mg though, but also whatever else is in the additives, chloride for example is really common and could add to salinity as well, I think maybe depending on what it reacts with in the water.

 

Magnesium would be magnesium sulfate and magnesium chloride. The chloride ions, free in the water, would meet up with free sodium ions from the sodium (bi)carbonate, and raise salinity.

 

good point, but not entirely relevant - at least from how I look at it. I am using calcium chloride, but the daily dose of that is a constant. I did not increase nor decrease that.

Only added Mg. (a Mg Chloride and Mg Sulfate blend) I'm not saying, necessarily, the sg increase is soley from Mg atoms, but the Ca levels (AWA the Mg Chloride levels) are directly controlled by the Mg levels. Therefore the fluctuations in sg are directly controlled by the fall and rise of Mg.

And it is that relationship I am displaying here.



FWIW I am using BRS 2-part.

 

I was just saying that the magnesium supplement you used added a lot of sulfate and chloride which also helped raise the salinity. It obviously had some effect on your Ca levels as well but I think that the chloride/sulfate in your Mg supplement probably had a large impact on your salinity as well as the Mg itself, and I don't think the Ca change had a large impact on salinity.

Chemistry and the Aquarium

Changes in chloride and sulfate levels also have a large impact on overall salinity as well as changes in Mg.

Randy Holmes-Farley - Chemistry In The Aquarium

That's my understanding anyway.