Improper mix of Mg Supplement


New member
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Years ago I used to dose my 125g reef tank with a one part Kent Marine Magnesium supplement. I wasn't able to achieve a consistent regular dose until I purchased in 2011 a dosing pump. Over time this lead to an increased use (and expense) of Mg. I started buying a two part mix for a Mg supplement; Mg Chloride and Mg Sulfate and preparing the solution myself.

At that time I had read a recipe on the sellers website of the following:
7-1/4 cups Mg Chloride
3/4 cup of Mg Sulfate
1 gal RODI H20

After playing around with the dosing amount I settled upon a volume that yielded a Mg level in my tank of ~1420. Over time I adjusted to get the level to the hi 1300's but sometimes it would fall to the low 1200's maybe even the high 1100's. During this time my calcium levels would move between the low 500's to the low 400's and my alk would range between 8 and 10.

Just recently I received a new order of Mg Chloride from BRS and I was reading the label. To my surprise I saw that the recipe read as follows:
5 cups of Mg Chloride
3 cups of Mg Sulfate
1 gal RODI H20

For the past year and a half I started having a very bad problem in my tank whereby many of my SPS corals started losing their tissue. I have been fighting this battle and I can't seem to put my finger on why. I have tried my best to keep all parameters (NO3, PO4, Calc, Alk, pH, Salinity, etc) all in the proper ranges, and for the most part have done that.

Do you know what affect could I have been causing to my tank by dosing it for the last 2 years with the incorrect recipe of Mg supplement as I have been doing above. Almost an 8:1 ratio of Mg Chloride to Mg Sulfate when it should've been 5:3?

Any help would be greatly appreciated.


Bomb Technician (EOD)
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There are different recipes for Magnesium sups. And reasons behind it, called balanced. First, you are not measuring Chloride or Sulfate and there are different formulations for both chloride and sulfate, ie, mono, bi, hexa, hepta, etc ( <--water ). When you up the sulfate, sulfate levels will get higher in proportion to chloride, unless you do a min of a 30 % WC/ m. For example, chloride in seawater is ~ 19,000 ppm and sulfate ~ 2,700, a ratio of 7:1. In your first recipe there will not be as much in off set in the ratio, in the second it will be more. Meaning, adding 100 ppm to each is allot in ratios. 19,100 / 2800 = 6.8:1, add another 100 ppm 6.6:1, then 6.4:1

Please take a read of this:

Where your came from

7-1/4 cups Mg Chloride
3/4 cup of Mg Sulfate
1 gal RODI H20
Do-It-Yourself Magnesium Supplements for the Reef Aquarium

I have no clue why BRS is that high. It is them in error not Dr. Randy Holmes Farley.

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