Magnesium-To dose or not to dose?

[scubaguy2010]

Let me start by quoting from Eric H. Borneman's book "Aquarium Corals-Selection, Husbandry and Natural History" who appears to be a very accomplished marine biologist.

Page 357 - "Magnesium is deficient in some salt mixes, and iron is depleted from typical reef aquariums rather rapidly. However, it is not at all certain why this is occurring. One cannot assume biological uptake, unless an organism known to utilise a particular element is present; more is unknown about such aspects of reef systems than is known........However, any need for supplementing these various elements for corals has simply not been adequately established. Every day seems to bring out avid hobbyists proclaiming that a certain element is directly responsible for some wondrous effect. With no disrepect intended for such enthusiasm, I would point out that commercial salt mixes already provide most major and minor trace element constituents of seawater in amounts that far exceed the levels in natural seawater. Assuming that regular, partial water changes are being performed, replenishment of trace elements with additives is probably not justified and, in some cases may even be poisonous........To repeat, corals require an aquarium, seawater at the right temperature and salinity, water flow, light, food, bicarbonate/buffer and calcium. Period. No other equipment, apparatus, magic potions, pills, voodoo, prayer, or other sacrifices are necessary."

So, in light of the above, I ask, does anyone dose magnesium and why? Has anyone actually witnessed their magnesium levels drop, regardless of partial water changes, and needed to replenish them with a dosing regime?

[marvelousone]

I have seen my levels drop and i dosed. I went a club meeting and red sea rep was there. They say to do less water changes and dose. mag. is needed to keep calcium and alk. from bonding together so coral can take cal. in. Ever since then I started doing that and my tank has done very well. I started with little frags and ever thing is growing better than before. For me it is working.

[bertoni]

Some people report drops, and that makes sense. Corals and coralline do consume magnesium in place of calcium:

http://www.advancedaquarist.com/2003/10/chemistry

That said, I never saw any significant magnesium drop due to consumption. Every tank will be different in that regard.

[Steve Wright2]

I had a full SPS set up over 12 months, dosing calcium and alkalinity on a daily basis
but for those 12 months my Mag stayed between 1420 and 1440 (Salifert)
then during last 12 months I began to notice a drop in magnesium, despite continuing with the 5% weekly water changes
for the 1st couple of weeks I had missed it, due to only testing Mag monthly due to fact for over a year it never seemed to move
it was at 1380, which is OK I know
but I dosed to get it back to 1440, and nowdays dose enough to replace 20ppm or so every other week

my coralline has really taken off, and requires weekly maintenance to prevent it claiming the front and side glass

so yes, I dose, but for a long time, there was no need to

as Bertoni states, it varies between set ups

Steve

[scubaguy2010]

It sounds like, "it depends what your tank needs". I guess, keep testing and make a decision based on the results......don't forget about it.

I would still welcome to see more comments based on personal experience.

Thanks.

[ReefTeacher]

Why would you not strive to have NSW levels of any parameter you can measure? If your tank is consuming Mg, whether from biological use or abiotic precipitation, why would not you try to replace what is used? I have never heard of anything suffering because the water chemistry was too close to natural levels. MgCl2 is cheap so why not replace what is used?

Of course, if you levels never drop, there is no need to suppliment....

[coralsnaked]

Yes I dose Mg because I like to keep my levels at 1450 ppm. I find the slightly elevated levels tend to prevent precept on my 450 ppm Ca and 9.0 dKH Alk. However w/ all my supplements I dose in the saltwater after mixing to bring them to the levels I desire, and only test display after weekly water changes. I find very little supplementation is needed directly in the tank.

Also the only time I’ve encountered a severe algae outbreak was when I had an Mg level fall below 1100 ppm on a smaller tank. Can't swear that was the reason, but that was the single thing I could find that was out of parameter. It was on an established tank w/ no new additions of coral or critters.

Since then I decided that Mg levels are as important as the other two foundation elements, and it is my understanding that Mg does play some role in the uptake of Ca. Do not really know what the direct connection is, whether it is utilized w/ Ca uptake or in lieu of Ca uptake. I’m sure one of our resident chemists would know. I have since observed some corals, especially LPS fleshy corals tend to “color up” a little w/ levels at 1450 ppm. Have also noticed some corals fade in color when levels exceed 1800 ppm as when treating for Bryopsis. This was however, a temporary change, the color did return when levels were reduced.

Merry Skerry

[tmz]

NSW has a magnesium level of around 1280 ppm, living things use it. Salt mix adds some back at varying levels depending on the mix in use,the frequency of water changes . Some comes in with food too. . Some don't need to ever dose it; others do but not with regular frequency. Recommended levels are 1250ppm to 1350ppm. It also effects the rate of calcium carbonate precipitation so in that way ties into the amount of available calcium and carbonate in solution.
Eric Borneman doesn't recommend chloride or sodium in that quote either but they are a major part of seawater as is magnesium.

This has more:

http://www.advancedaquarist.com/issues/oct2003/chem.htm

[BlakDuc]

How old is that book? A lot has been learned and continues to be learned since he probably wrote that book.

A lot of good input in this thread, yes, Mg does play a pretty important part with the CA/Alk bond.

[Dapg8gt]

I only dose it when I need to. Which is usually every few months to keep me from 1350-1400+.. When I changed salt mixes it did change on frequency.. I only test monthly for mag and weekly for the others..

[tmz]

I have a high demand system but regualr frequent water changes amounting to a total of about 40% per month with a salt mix relatively high in magnesium make it unecessary for me to dose it except 50ppm once per year or longer. I test it once every month or two.

[jc-reef]

Yes I dose Mg because I like to keep my levels at 1450 ppm. I find the slightly elevated levels tend to prevent precept on my 450 ppm Ca and 9.0 dKH Alk. However w/ all my supplements I dose in the saltwater after mixing to bring them to the levels I desire, and only test display after weekly water changes. I find very little supplementation is needed directly in the tank.

Also the only time I’ve encountered a severe algae outbreak was when I had an Mg level fall below 1100 ppm on a smaller tank. Can't swear that was the reason, but that was the single thing I could find that was out of parameter. It was on an established tank w/ no new additions of coral or critters.

Since then I decided that Mg levels are as important as the other two foundation elements, and it is my understanding that Mg does play some role in the uptake of Ca. Do not really know what the direct connection is, whether it is utilized w/ Ca uptake or in lieu of Ca uptake. I’m sure one of our resident chemists would know. I have since observed some corals, especially LPS fleshy corals tend to “color up” a little w/ levels at 1450 ppm. Have also noticed some corals fade in color when levels exceed 1800 ppm as when treating for Bryopsis. This was however, a temporary change, the color did return when levels were reduced.

Merry Skerry


I agree with this and witness very similar observations with my tank. I find my Ca levels fall off and cause some unstable Alk levels as well when Mg falls below 1300. I try to keep mine at 1400+ which in turns seem to keep my Ca & Alk stable. I also find that the Mg usage by my tank will vary from time to time.

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