kalkwasser and magnesium

[GSnake]

these past few weeks ive been trying to raise my magnesium, it dropped by nearly 300, according to both test kits I have. I cant fid the reason for the drop since its never happened before like this. my lines are clear..

"Magnesium depletion is commonly associated with the use of kalkwasser ".
"In-fact, using kalk can actually lower magnesium levels by causing magnesium to precipitate out of solution as magnesium carbonate (MgCO3). Thus maintaining adequate levels of magnesium is crucial when dosing kalk." https://www.reefsupplies.ca/online-store/blog/2016/10/03/a-keep-it-simple-guide-to-dosing-magnesium/

this is the first time I came across this information, since my kalk is in ATO I thought this might be the issue. however ive been using kalk for a while now, and no such thing happened before.
also is this true? its not stated widely, actually its the first time ive heard of it being possible.

 

[Randy Holmes-Farley]

these past few weeks ive been trying to raise my magnesium, it dropped by nearly 300, according to both test kits I have. I cant fid the reason for the drop since its never happened before like this. my lines are clear..

"Magnesium depletion is commonly associated with the use of kalkwasser ".
"In-fact, using kalk can actually lower magnesium levels by causing magnesium to precipitate out of solution as magnesium carbonate (MgCO3). Thus maintaining adequate levels of magnesium is crucial when dosing kalk." https://www.reefsupplies.ca/online-store/blog/2016/10/03/a-keep-it-simple-guide-to-dosing-magnesium/

this is the first time I came across this information, since my kalk is in ATO I thought this might be the issue. however ive been using kalk for a while now, and no such thing happened before.
also is this true? its not stated widely, actually its the first time ive heard of it being possible.

I don't believe it is accurate, although it is hard to disprove entirely. If one did drop magnesium by 300 ppm this way, calcium MUST rise by nearly 500 ppm. That huge rise does not appear to happen, only a small rise that comes from incorporation of magnesium into calcium carbonate in corals, coralline algae, and abiotic precipitation.

However, one reason that magnesium will decline is that you are adding only calcium and alkalinity, but magnesium is incorporated into skeletons and coralline algae and abiotic preciptiation. Hence it is consumed and you are not adding any. Consumption varies but is on the order of 1/10th of the calcium consumption. If you consume 10 ppm of calcium per day, that might be about 1 ppm per day.

 

[GSnake]

okay, actually 2-3 months ago cal did spike that high, due to a dosing accident- its been normal for the past month or so - on all parameters . then this past week my mg took that 300 dip I posted about. why this delay for balance?
by the way im dosing cal/alk/mg/amino

 

[Nano sapiens]

I've had some unexplained rapid drops in Mag levels over the 12 years my small system has been running while using kalkwasser exclusively. But nothing nearly as drastic as what you are describing (more in the order of dropping 50 - 75 ppm in a week). I'll raise it back up to around 1300 - 1350 ppm and then I'll have long periods of the usual slow depletion rates again.

I have noticed that the drops tended to occur when Mag was hovering around 1200 - 1250 ppm or so. What level did you have before you saw the 300 ppm drop?

 

[GSnake]

im looking at my log and noticed 1750+ mg at the same time of my cal spike too. (march 6). but I did not overdose MG supplement*

anywho my average mg is 1350 then week to week it can be +/- 50, usually from 1300-1350.
so may 12 1300mg- im expecting it to be 1350 next week, trend wise
may 19 1150 mg +2ml (= 9ml)
may 21 1050mg +3ml (=14ml dose currently)

 

[Randy Holmes-Farley]

anywho my average mg is 1350 then week to week it can be +/- 50, usually from 1300-1350.

That range is a testing issue, not an actual up and down of magnesium by 50 ppm. There is no way for it to decline 50 ppm in a week, and unless you add a lot, same about the rise.

 

[Randy Holmes-Farley]

But nothing nearly as drastic as what you are describing (more in the order of dropping 50 - 75 ppm in a week).

I think that too is a testing error.

let's look closer...

If you added enough limewater (kalkwasser) to maintain 2 dKh per day (that's 1.75% of the total water volume in saturated limewater each day), and somehow every bit of it precipitated as pure magnesium carbonate (very unlikely since it is more soluble than calcium carbonate), and so no actual alkalinity addition took place, then you would only consume 63 ppm of magnesium in a week.

Thus I think this hypothesis of magnesium consumption by precipitation of magnesium carbonate (rather than calcium carbonate with a little bit of magnesium in it) requires too many extreme assumptions to explain what folks see, and does not fit with the actual preciptiate that is observed when adding hydroxide to seawater (magneisum hydroxide, which redissolves as it mixes in and the ph is lowered).

https://www.jstor.org/stable/1536800?seq=1

 

[Nano sapiens]

I think that too is a testing error.

let's look closer...

If you added enough limewater (kalkwasser) to maintain 2 dKh per day (that's 1.75% of the total water volume in saturated limewater each day), and somehow every bit of it precipitated as pure magnesium carbonate (very unlikely since it is more soluble than calcium carbonate), and so no actual alkalinity addition took place, then you would only consume 63 ppm of magnesium in a week.

Thus I think this hypothesis of magnesium consumption by precipitation of magnesium carbonate (rather than calcium carbonate with a little bit of magnesium in it) requires too many extreme assumptions to explain what folks see, and does not fit with the actual preciptiate that is observed when adding hydroxide to seawater (magneisum hydroxide, which redissolves as it mixes in and the ph is lowered).

https://www.jstor.org/stable/1536800?seq=1

I would have to agree that that is a very strong possibility. I've found testing for magnesium rather 'touchy' with any of the hobby grade kits we typically use. I've gotten more consistent results over the years by being very accurate/careful when collecting the water sample, adding the reagents and the whole testing process in general.

Going way back, I tested Mag with my RedSea kit right before sending off my water sample to Triton for ICP testing. There was a big discrepancy in the order of 150-200 ppm between my testing (lower) and theirs (higher).

 

[GSnake]

sort of contrary to what you said about hydroxide being soluable when mixed in with seawater.. is this post from seachems' reef advantage magnesium, I found while shopping for mg.

"Kalkwasser, for instance, precipitates magnesium as magnesium hydroxide while excess carbonates precipitate it as magnesium carbonate. In both cases, this means that magnesium that was present in the water is now unavailable. Of the two, magnesium hydroxide and magnesium carbonate, the former is more problematic; it is extremely insoluble. Once magnesium has precipitated as magnesium hydroxide, it will never redissolve. Magnesium carbonate will redissolve; however, it does so slowly. So, while it will go back into solution, there will be a significant portion of time in which magnesium levels are depleted."

that is the last of the posts I saw regarding this..
i think I shall just double up my magnesium dose it seems

and I really cant believe you had a 200 ppm difference between tests. I"m sort of experiencing the same thing maybe

 

[Backreefing]

I thought to ask this question on this thread because it is all about mag.
I have never dosed magnesium yet my aquarium is 1500 + ( aqua forest ) . My salt mix is not that high and I have only dosed Kalkwasser, (in the past . ) could this mag be released from crushed coral gravel? Because it’s odd man out ? There’s no other supply of magnesium. BTW my salt mix is Red Sea blue bucket.

 

[Randy Holmes-Farley]

sort of contrary to what you said about hydroxide being soluable when mixed in with seawater.. is this post from seachems' reef advantage magnesium, I found while shopping for mg.

"Kalkwasser, for instance, precipitates magnesium as magnesium hydroxide while excess carbonates precipitate it as magnesium carbonate. In both cases, this means that magnesium that was present in the water is now unavailable. Of the two, magnesium hydroxide and magnesium carbonate, the former is more problematic; it is extremely insoluble. Once magnesium has precipitated as magnesium hydroxide, it will never redissolve. Magnesium carbonate will redissolve; however, it does so slowly. So, while it will go back into solution, there will be a significant portion of time in which magnesium levels are depleted."

that is the last of the posts I saw regarding this..
i think I shall just double up my magnesium dose it seems

and I really cant believe you had a 200 ppm difference between tests. I"m sort of experiencing the same thing maybe

They are most certainly incorrect. Magnesium hydroxide is readily soluble in seawater.

The Oceans Their Physics, Chemistry, and General Biology

The Oceans Their Physics, Chemistry, and General Biology

from it:

"The apparent supersaturation of the calcium carbonate is discussed in the preceding pages. The ionic products of the other salts do not approach their solubility products. At pH higher than 9.0 the ionic product of Mg(OH)2 will exceed the solubility product, and hence removal of CO2 may result in precipitation of magnesium hydroxide as well as the carbonates. "

Thus, unless the pH is above pH 9, magnesium hydroxide is readily soluble in seawater.

 

[Randy Holmes-Farley]

I thought to ask this question on this thread because it is all about mag.
I have never dosed magnesium yet my aquarium is 1500 + ( aqua forest ) . My salt mix is not that high and I have only dosed Kalkwasser, (in the past . ) could this mag be released from crushed coral gravel? Because it’s odd man out ? There’s no other supply of magnesium. BTW my salt mix is Red Sea blue bucket.

Most likely it is test error. Magnesium will not appreciably rise from gravel. -

 

[GSnake]

Thus, unless the pH is above pH 9, magnesium hydroxide is readily soluble in seawater.

sounds realistic to me now.
this is the second time with unrealistic or inaccurate from seachem, I thought they were a large responsible brand, or / and , its just my naivety to reefing. (first case was nitrate test kit instructions)

to wrap things up with magnesium... I have been using only magnesium chloride hexahydrate (aquaristik) thus far, however your recipes and the mixes sold out there are a combination of MgClH and magnesium sulfate - to provide an ionic balance.
is not having an ionic balance detrimental to the tank, and to what degree? maybe less effective? in relation to only using the MgClH as a mg source.

I have never dosed magnesium yet my aquarium is 1500 + ( aqua forest )

id just test every now and then, its bound to drop and show up on the test. or try different test kit / ask LFS to test.

 

[GSnake]

after reading your recipe again, I think im just going to go this route instead ---

I already have Epsom and mgclH, but is this mixture really ~12,433 PPM / Litre.. 12.433 ppm/ml / 25
= .50 ppm/ml (in 25gallons)
like in comparison with RS -
1g will raise the Mg level of 100 liters (25 gal) 1.34ppm.
1 kg will make 1.7L of stock solution.
so = .79 ppm / ml

sounds right? so its about half as strong.

I can finally find calcium chloriide now too, so I will be trying the diy for this ! - do you dose strontium? or just water changes -
im currently using RS calcium (with strontium)

 

[Nano sapiens]

They are most certainly incorrect. Magnesium hydroxide is readily soluble in seawater.

Astounding how much incorrect and/or misapplied information is 'put out there' from companies that should have a better/clearer understanding regarding the products they sell. No wonder even experienced reef keepers can get tripped up on occasion, what more new people coming into the reef keeping hobby.

 

[GSnake]

heres the dowflake Xtra I found that I might be able to get my hands on ,

Dow 20kg Calcium Chloride | Home Hardware

Get the DOW 20kg Calcium Chloride at your local Home Hardware store. View online and pick-up in store.

www.homehardware.ca

is this stuff ok?
here's some details on what looks like the same thing from another website

DOWFLAKE™ XTRA 83-87% CALCIUM CHLORIDE

DOWFLAKE™ Xtra 83-87% Calcium Chloride is a purified inorganic salt produced by removing water from a naturally occurring brine solution. Unlike other processes used to produce calcium chloride, the brine process does not involve reactions with chemicals such as hydrochloric acid or ammonia.

www.kpmindustries.com

Magnesium chloride

Magnesium Chloride performs better, is safer and kinder to the environment. Its secret - total ice control. Magnesium Chloride melts effectively down...

www.rona.ca

unfortunately I haven't been able to find magflake (in Canada at least), and will probably settle for aquaristik pouches
the link above is the closest thing I can find in store

 

[alimac122]

Wait... who said magnesium hydroxide wasn’t soluble.

[OH-] is insanely soluble... because... ya know... H2O....

 

[Randy Holmes-Farley]

Wait... who said magnesium hydroxide wasn’t soluble.

[OH-] is insanely soluble... because... ya know... H2O....

Not all hydroxide salts are highly soluble. Both magnesium hydroxide and calcium hydroxide are poorly soluble in fresh water. That is why there is a 2 tsp/gallon limit to the solubility of kalkwasser (calcium hydroxide) in fresh water, and magnesium is not at all soluble in it.

 

[GSnake]

was able to find magflakes and dowflake xtra locally. (after a lengthy search of course)
will be making some diy today!
also making a diy gfo reactor while I was at it this weekend.