View Full Version : magnesium question....

12/06/2011, 05:21 PM
ok so i am confused... havent had a reef tank in more then 5 years and alot seems to have changed..so limeater works great much better then baking soda ever did for me.. i pre mix it with my makeup water and drip it in via an iv bag..... so ph is pefect now my guestion is magnesium how important is it.. i just read that i need to test for it and suppliment.. i have never dont that in the past..

tank is a 55 gallon reef ready with a 45 gallon sump.. 8 punds of uncured live rock and about 60 punds or so 3/4 in the ds tank of old live rock that is more like base rock.. system has been up for a more then two months..getting alot of coraline growth and there are 3 diff montis in there all growing.. the other corals and green stars and zoa and paly and mush.. not worried about them.. my tank is just soaking up the lime water mix i have to add it with almost all the make up water in full soluable concentration.. my guestion is.. what is magnesiums role and should i get a test and start dosing seeing how well the tank is doing and the amount of coraline algae and monti growth..

12/07/2011, 12:22 AM
Magnesium is consumed in small quantities by corals and coralline in place of part of the calcium in their skeletons. In some tanks, magnesium will drop enough to require supplementation. Magnesium acts to prevent calcium carbonate precipitation, so if the level gets very low, that can be a problem. This article might be a good place to start, if you want to do some more reading:


Randy Holmes-Farley
12/07/2011, 05:56 AM
If you do regular water changes with a high magnesium salt mix, you might never need to add any magnesium. But if you do little to no water changes or use a low to normal magnesium mix, you might benefit from measuring the magnesium and adding some if necessary. :)

12/07/2011, 03:40 PM
I aim to keep the Magnesium in my 120 around 1400ppm, to do so I add at least a cup of Magnesium Chloride weekly. My old 26 gal didn't require any Magnesium supplementation and I've used Reef Crystals the whole time, same RO, same fish, and only a few new coral frags so far. Any idea why one tank would be such a large consumer while the other was autonomous?

Randy Holmes-Farley
12/07/2011, 03:48 PM
The only magnesium sinks are calcium carbonate precipitation (like coral skeletons) and removal by water changes with a lower magnesium salt mix. I'm not sure why you are observing differences now.