Magnesium question

[AJT]

I have a 748 gallon tank mixed sps, lps, softies, fish

Amonia 0
NO2 0
No3 0
ALk checked this weekend at 10.54 Hanna - high
Calcium 390 trying to get this up which I think raised alk
Mg last check at 1000

I have been told that because the Mg was low that my constant calcium reactor drip has raised my alk too high.

I did a 160 gallon change on sat & a 180 gallon change on Sunday to get alk down.

Everything is looking pretty good.

to raise & keep MG at 1350 will take 7 gallons of BRS Mg. mix

Is there a more concentrated Mg that I can use ongoing?

Any comments welcome

[Randy Holmes-Farley]

Originally Posted by AJT

I have been told that because the Mg was low that my constant calcium reactor drip has raised my alk too high.

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Either you did not understand properly, or the speaker did not understand reef chemistry. Most likely the latter because somehow people have gotten the idea that low magnesium leads to "calcium precipitation" and they forget that alkalinity must be reduced in such a precipitate, and by a far higher percentage than calcium is.

What you cannot do (and apparently tried to do) is to raise calcium with a calcium carbonate/carbon dioxide reactor, because every 18-20 ppm boost to calcium results in a 2.8 dKH rise in alkalinity. So any significant calcium boost needs to be done with a calcium only supplement to keep alkalinity from getting too high.

[AJT]

Thanks for your reply.

So if I understand you correctly. I need to do water changes to get the Alk down to say 8 like I have been doing?

Raise the calcium with something like the Bulf reef supply 2 part calcium (I have), then use the reactor to keep it up?

Magnesium- What is the best way to keep mg up on 748 gallons? What would be the best additive without having to dose 7 gallons? More concentrated brand.

Thanks again Randy

[Randy Holmes-Farley]

I wouldn't reduce alk by water change. I'd do it by stopping the reactor and letting it fall on its own. Many salt mixes have higher alk than your currently at.

My DIY magnesium supplement (which BRS sells ingredients for) is a fine best choice, and concentration is unimportant. All it means is you add mroe or less water to the solids.

FWIW, with magnesium that "low", I'd be worried that it may be testing error and not just low magnesium.

This has more:


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


and

Solving Calcium and Alkalinity Problems
http://www.advancedaquarist.com/issues/nov2002/chem.htm

[AJT]

Thanks,

I will read up on the links tonight.

[Randy Holmes-Farley]

Originally Posted by AJT

Thanks,

I will read up on the links tonight.

Good luck.

[feh]

Originally Posted by Randy Holmes-Farley

Solving Calcium and Alkalinity Problems
http://www.advancedaquarist.com/issues/nov2002/chem.htm

This is one of my favorite articles.

[bongarone]

You can raise your calcium only by adding only the calcium part of the "2-part" system. Your reactor is adding both, so I'd stop the reactor temporarily.

Your magnesium is a touch low as well I think, but that's a separate issue.

[MarkGP]

Also, once you get the magnesium to where you want it you can add dolomite to the calcium reactor media (around 15%) to maintain the mag.

[AJT]

I stopped the reactor when I saw the alk climbing. It is a deltec reactor & I am using their media.

What alk should I shoot for with SPS.LPS, softies etc...

I will test again tonight or tomorrow & use the BRS calcium to get it back up.


I really need to read up on alk/calcium/ph relationships. I have read thru some of Randys work in the past but need to brush up & find the "Cliff notes" on it.

[Randy Holmes-Farley]

I generally recommend that folks aim for 7-11 dKH, unless it is a ULNS system, in which case, I'd aim for 7-8 dKH.