Adding Mg via Ca reactor plus low Mg question

[Tech Diver]

I recall hearing somewhere that you can supply Magnesium to your tank by adding pure Dolomite to your reactor media. Is this true? If so, this would be a very convenient way of dosing for me.

Since I moved from my 29g to my 58g two months ago, I am struggling to keep my Mg above 1100, which in turn is affecting my Ca level (I believe). I add ESV B-Ionic Mg, but perhaps at a too conservatively low level. My tank is primarily LPS with some SPS and I guess I am just not keeping up with the demand. Any insight is welcome. My tank parameters are:

Tank 58g
Sump/refugium 20g
SG 1.025
pH about 8.20 to 8.41 (daily swing)
Ca 380 ppm
Alk 3.8 meq/L
Temp 79-80 deg F

Note: I use Tropic Marin salt

[bertoni]

I don't run a reactor, so I am sketchy on the details, but I didn't think that dolomite worked all that well, for solubility reasons. I think there's a Zeo media that will add magnesium.

The tank probably needs more Mg supplement. This calculator will help with a dose:

http://home.comcast.net/~jdieck1/chem_calc3.html

I wouldn't add more than 100 ppm per day.

[Randy Holmes-Farley]

If you go the reactor route, be sure to get the magnesium where you want it first. You cannot use that method for a big magnesium boost (or even a small one) as it will also boost alkalinity too much.

[Tech Diver]

Thank you both for the info. I definitely don't want to raise my alkalinity any more than it is.

[Randy Holmes-Farley]

You're welcome.

These have more that may be useful:

Do-It-Yourself Magnesium Supplements for the Reef Aquarium
http://reefkeeping.com/issues/2006-07/rhf/index.php

Magnesium in Reef Aquaria
http://www.advancedaquarist.com/issues/oct2003/chem.htm

Magnesium and Strontium in Limewater
http://www.advancedaquarist.com/issues/dec2003/chem.htm

A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH
http://reefkeeping.com/issues/2006-06/rhf/index.php

[cato]

I did what Randy said. Brought my mag levels up to par and added Zeomag to my reactor media. I used about 4/5 Ca media to about 1/5 Zeomag media. It works great. I'm about due to add more media and need to adjust the mag amount a bit more than 1/5th of the chamber volume due to the fact it very slowly drops from about 1350 to around 1200 in a couple months. HTH :)

[Tech Diver]

Thanks Cato for the Zeomag suggestion. I am not familiar with this product and will study it further. It sounds exactly like what I've been looking for (providing it does not raise my alkalinity).

Also, thanks Randy for the links. The articles were very helpful and I have a much better understanding of the chemical interactions involved.

Peter

[MarkGP]

I run Dolomite in my calcium reactor at a ratio of 10 parts reactor media to one part dolomite. I've been using this for 2 years now and have never had to supplement mag as it stays at 1350.