Adding Magnesium (hydroxide or sulphate) to kalkwasser

[murinus]

Hi all,
i've recently found a couple of guys on the italian Newsgroups and Forums who add Magnesium to their KW stirrers.
Since i haven't read anything like that anywhere else and since i know people who like playing playing "the little chemist" adding any sort of thing to water (from amino-acids to vitamins and anything in between like fluoride drops and human growth hormone (not joking!)) stating their corals now grow better (yeah dude, is not the 400w halides, the 1000dollars skimmer, and calcium reactor, it's the magical concoction you just invented silly boy).
Anyway, has this practice of adding Magnesium to Calcium hydroxide any sense or is it just plain crap?
Thanks a lot in advance

[Randy Holmes-Farley]

Magnesium is not soluble in limewater. It will settle out as insoluble magnesium hydroxide. If you dose it cloudy,then some magnesium will get to the tank, but if it is clear and settled limewater (my recommendation), then little to none will reach the tank.

I discuss it in this article:

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

[murinus]

Thanks a lot for this enlightening reply

Here every day a guy wakes up with a brilliant idea. It is usually a mr.no-one who comes out with a magic recipe to grow corals faster, and all of a sudden it becomes a craze. He lives his 15 minutes of fame and he's happy.
I'm just curious what comes next, maybe habanero chili peppers in the sump to discourage diseases and raise corals metabolism

Is there any chemical at all, besides vinegar, that can be added to KW without precipitating or becoming useless in a short time?

[Randy Holmes-Farley]

To reduce the pH of limewater? No, not really.

Some can be added to it if you want. Strontium, for example.

[murinus]

I'm sorry if i'm bothering you on this topic, but to acquire some solid knowledge is almost impossible where superstition rules, such as in the forums i read. Therefore i'd be thankful if you can clear these two points.
First one is about addition of Magnesium to KW. One guy says: "Ok, if solution is saturated, then nothing else (read Magnesium) can easily pass into solution, BUT if the two compounds (Calcium and Magnesium Hydroxide) are mixed together BEFORE having a full strenght calcium hydroxide saturated KW, THEN, some magnesium would stay into it. Does his theory make any sense, not chemically, but aquarium wise?
Also, you told me strontium can be added to KW, so this is an option to dose it into our tanks, but, given the two options, isn't anyway better to dose Strontium in the old fashioned way of putting a few drops of a commercial/homemade supplement directly into the sump or in the flow of a pump once a week?
Again, thanks a lot in for the preciuos advice you gave so far, and in advance for the questions i just made

[Randy Holmes-Farley]

BUT if the two compounds (Calcium and Magnesium Hydroxide) are mixed together BEFORE having a full strenght calcium hydroxide saturated KW, THEN, some magnesium would stay into it. Does his theory make any sense, not chemically, but aquarium wise?

If you are talking about dissolving the magnesium, then no, it does not make sense unless the limewater is very, very dilute. Say, 1 teaspoon in 50 gallons of fresh water. I didn't show the graph in that article, but in this article I show the solubility of magnesium as a function of pH, regardless of the order of mixing.

Also, you told me strontium can be added to KW, so this is an option to dose it into our tanks, but, given the two options, isn't anyway better to dose Strontium in the old fashioned way of putting a few drops of a commercial/homemade supplement directly into the sump or in the flow of a pump once a week?

I don't dose strontium at all (water changes keep it up in my tank), but either way is fine if you choose to do so. :)


The Self Purification of Limewater (Kalkwasser)
http://www.advancedaquarist.com/issues/may2003/chem.htm

At pH values above 10.5, the magnesium concentration is very low. Saturated limewater is about pH 12.5. Half saturated limewater has a pH still above 12. At those values, the solubility of magnesium is far below 1 ppm.

[murinus]

Again thanks a lot for the answer to my question, and for the link to the very interesting article you pointed me to
It's great to read from people like you who have rock solid scientific knowledge, opposed to the moron alchimists and their witchcraft recipes for "a better reef" we have in Italy

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)

[jimbo045]

I think Magnisium is a good thing to add, but just a little.

[Randy Holmes-Farley]

It is fine to add magnesium to a reef aquarium, but adding it to limewater, if it is allowed to settle out, is not useful. :)