I have had a long history of dealing with low magnesium. Mine was suuuper low for the first year, like 600-700. !@! I bought another test kit and it read about the same. the reef calculator said that I would need to add 3 or 4 bottles of Tech M to my 34 gallon. this seemed Nutz. I also would dose a bunch, and it would rise somewhat, but then would fall again.
The second test kit came with a reference solution. It tested right on. I investigated using solid magnesium hexahydrate and found that it was a reasonalbe cost. The shocking thing, is that a 50 gallon tank may have 6 pounds of magnesium dissolved in its saltwater. !! That's a lot.
I never understood why mine was sooo low. I asked on reef central, and unfortunately, everyones explanation was along the lines of... that's impossible. You are doing something wrong. There is no way... In other words, if they couldn't understand how it could happen, then it must not be happening. Kind of an arrogant attitude when you step back and look from afar.
I ended up using the reef calculator and found that 212 grams of mg would theoretically raise my 50 gallon volume by about 100 ppm. I weighed it out, adn that's exactly what it did. Over a few weeks, I brought it up to about 1,400 ppm. At one point, it dropped about 200 points in about 2 weeks. Impossible, they said.... I dosed it again, and it has been fairly stable since.
I say believe your test kit. To be sure, read your instructions and follow them. Also, test against a reference soln if you have one. Then calculate it and dose it up to where it needs to be. A super elevated mg level, if you are wrong will not hurt much anyways, I bet. They do it to treat bryopsis.
Use the force....
