Tell me about magnesium!

[Delphinus]

I think our understanding has progressed in those years Brad. I started looking at Mg a long time ago, 5 or 6 years easily so it feels a little old hat to me now but it was an eye opener when I did start looking into things.

Now .. I can't honestly say I've noticed a difference with corals and Mg levels. The things I have noticed about Mg however:

1) Easier to maintain balanced Ca/Alk levels when Mg is right. When Mg is too low, it feels like I'm adding way more calcium to get it to raise. Also, a lot less precipitates out on powerhead impellers and so on. My salt mixing rubbermaid always had a 2mm thick layer of calcium encrustation over the whole surface and that stopped once I started mixing Mg into my makeup water before adding salt.

2) A.R.M. reactor media outputs a reasonable level of Mg so if you're using A.R.M. I would suggest that's why your Mg level in the tank is a solid "not bad" without even trying. You can also add Mg crystals from KZ to your media if you wish it to output a higher Mg but I always did find that Mg in my tank was never bad when I ran a reactor, it was things like my makeup salt had it too low and water changes were throwing the levels off.

3) I do notice when my Mg is low in the tank because the anemones don't seem to open as much. No idea why they care about Mg (ie. the biology behind this) but they do. I've seen it enough times to have a slight empirical basis to the observation. So having Mg at proper levels really doesn't hurt.

and

4) Although 47 tonnes in a year might be a slight exagerration nevertheless it is absolutely shocking how much Mg media it takes to raise Mg in a tank. A lot. I found with liquid additives I'd have to use up an entire $30 bottle to raise 24g of water change water to bring it from say 1100 (or whatever the starting point, depends on the salt I'd be using) to 1400 which is where I like my water change water to be. $30 per w/c is not sustainable so I switched to bulk and man I am going to miss LittleSilverMax/ChemMaster VERY much in this regard because buying from him was several orders of magnitude cheaper than bulkreefsupply.com. I just ordered some from BRS and the shipping was killer: I won't be buying bulk chems from them again. Off to Univar for me from now on.

5) I find that Mg depletion does occur in a system that also uses up Ca and Alk but it's a fraction of the depletion rates of Ca and Alk. So it's not really necessary to dose the tank unless you really want to - it's easy enough to maintain proper levels using water changes and tracking the Mg going in via w/c.