Magnesium? How often?

Randy Holmes-Farley · Sep 5, 2015

ReefMadScientist said:
@Randy Holmes-Farley
@Russ265

I didn't want to start a new thread. I just have one question. When you dose Mg does that raise Alkalinity and or Calcium? I only have to dose Mg maybe once every few months but just curious.

Thanks!

No, it has no direct impact on either one. If you add enough, it can reduce the ongoing demand for both through abiotic precipitation on heaters, pumps, etc.

MasterBlaster1 · Feb 9, 2022

I have a very weird issue with Mg . I have a 400 l pool with a lot of surfaces (shallow reef) and I don't clean the windows (grow tank) . My mg drops 40 ppm every 5-7 days if not added. I don't have clams, only corals. I am surprised by the need for so much Mg. Is this normal or some kind of precipitation or reaction. In the past, I dosed Kalk in a no-flow area and I understand that this reduces Mg by creating magnesium hydroxide. What can you tell us about this?

@Randy Holmes-Farley

Randy Holmes-Farley · Feb 9, 2022

MasterBlaster1 said:
I have a very weird issue with Mg . I have a 400 l pool with a lot of surfaces (shallow reef) and I don't clean the windows (grow tank) . My mg drops 40 ppm every 5-7 days if not added. I don't have clams, only corals. I am surprised by the need for so much Mg. Is this normal or some kind of precipitation or reaction. In the past, I dosed Kalk in a no-flow area and I understand that this reduces Mg by creating magnesium hydroxide. What can you tell us about this?

@Randy Holmes-Farley

How long have you been monitoring it?

What is the alk and calcium demand in that tank?

There's no substantial mechanism to drop magnesium by 40 ppm without dropping calcium by something like 400 ppm and alkalinity by 60 dKH.