magnesium …

[525]

hallo Boomer …
I need your help about the magnesium …
.. do I have to relate it with specific gravity ( example 1026 SG – 1280mg ) or with calcium ? ( mg=3X ca )
thank you in advance

 

[MikeS]

I'll take a stab at it...

Natural seawater has a Mg level of around 1260-1300 at 35ppt salinity (1.026 SG)...to figure the Mg content at a certain specific gravity, I convert SG to salinity, divide the result by 35 and then multiply that number by 1280...that gives you a pretty close estimate of where Mg should be at a certain SG. For Mg-Ca-Alk relationships...I just use this reef calculator...

http://home.comcast.net/~jdieck1/chemcalc.html

hope this helps...

MikeS

 

[525]

thank you MikeS !

for example .. if I have 1024 SG my salinity is 34 … and my correct mg have to be 1243 ppm
is that correct ?

 

[returnofsid]

Here's a newer version of the same calculator. It's a great improvement over the old one.

As for Mg, would it be safe to say that your Mg should be approx. 3 times your Ca? For instance, with a Ca of say...400, your Mg should be 1200.

 

[DonW]

Here's a newer version of the same calculator. It's a great improvement over the old one.

As for Mg, would it be safe to say that your Mg should be approx. 3 times your Ca? For instance, with a Ca of say...400, your Mg should be 1200.

3 times ca is fine.

Don

 

[returnofsid]

WooHoo, I got it right!! I'll learn this chemistry thing yet...thanks to A LOT of help from you Don!!!

 

[MikeS]

thank you MikeS !

for example .. if I have 1024 SG my salinity is 34 … and my correct mg have to be 1243 ppm
is that correct ?

Not a problem ...actually, at 1.024SG, your salinity is 32ppt...Specific Gravity and Salinity are two different measurements...

Specific Gravity to Salinity Conversion Chart

S.G. Salinity in PPT

1.0180 25
1.0185 25
1.0190 26
1.0195 27
1.0200 27
1.0205 28
1.0210 29
1.0215 29
1.0220 30
1.0225 30
1.0230 31
1.0235 32
1.0240 32
1.0245 33
1.0250 34
1.0255 34
1.0260* 35* Natural Sea Water
1.0265 36
1.0270 36
1.0275 37
1.0280 38
1.0285 38
1.0290 39
1.0295 40
1.0300 40

As for Mg, would it be safe to say that your Mg should be approx. 3 times your Ca? For instance, with a Ca of say...400, your Mg should be 1200.

Personally, I don't find it necessary to base Mg levels on Calcium levels, for a few reasons...#1, there is quite a bit more Mg in solution than Ca and carbonate alkalinity to start with, so you have a larger "safe zone" to work with...for example if you have a Ca level of 450ppm and the proper alkalinity level to balance, you really won't see much of a difference between an 1100ppm Mg level and a 1300ppm Mg level, both are basically sufficient for a near NSW salinity level and 450ppm Ca level. #2 it depleats in different ways and generally doesn't fluctuate as much as Ca levels. Its primary function in relationship to Ca and Carbonate Alkalinity is to inhibit precipitation of Calcium Carbonate, and it is able to do so at a fairly broad range of ppm levels, reguardless of the actual Ca or Carbonate Alkalinity levels.

here's some good reading on Mg in the reef tank...

http://www.advancedaquarist.com/issues/oct2003/chem.htm

http://reefkeeping.com/issues/2006-06/rhf/index.php

hope this helps...

MikeS