Kalkwasser and Magnesium... is it worth combining into one container for single dosing?

[Spicy Reef]

I've been doing a deep dive into alk, calcium, magnesium, precipitation etc... My most recent experiment has been to add magnesium to kalkwasser.

From everything I read around here.... DON'T do it... so of course I have to do the experiment. I'm finding there is only a little bit of truth in everything I've read.
Please set me straight on your experiments or maybe I'm doing something backwards here.

in the presence of kalkwasser, mag should precipitate out and ph/alk drop to unusable levels - This is what I read, but my experiment does not completely agree.

 

[HuduVudu]

@Spicy Reef what magnesium are you using?

 

[Garf]

I've been doing a deep dive into alk, calcium, magnesium, precipitation etc... My most recent experiment has been to add magnesium to kalkwasser.

From everything I read around here.... DON'T do it... so of course I have to do the experiment. I'm finding there is only a little bit of truth in everything I've read.
Please set me straight on your experiments or maybe I'm doing something backwards here.

in the presence of kalkwasser, mag should precipitate out and ph/alk drop to unusable levels - This is what I read, but my experiment does not completely agree.

Interesting test. I’d love to see @Randy Holmes-Farley explaination. I’m guessing the calcium hydroxide has settled out, leaving a magnesium excess.

 

[Garf]

I've been doing a deep dive into alk, calcium, magnesium, precipitation etc... My most recent experiment has been to add magnesium to kalkwasser.

From everything I read around here.... DON'T do it... so of course I have to do the experiment. I'm finding there is only a little bit of truth in everything I've read.
Please set me straight on your experiments or maybe I'm doing something backwards here.

in the presence of kalkwasser, mag should precipitate out and ph/alk drop to unusable levels - This is what I read, but my experiment does not completely agree.

For what it’s worth, I made an Aiptasia killing slurry with Kalk and Sodium hydroxide. Upon application in tank a translucent shell appears that condenses and hardens into a shell (or that’s how it appears to me). I assumed this shell was magnesium hydroxide. So, I added magnesium flakes to my slurry, to see what happened. I ended up with a few massive magnesium crystals growing at the bottom of the slurry. Threw it down the sink, lol

 

[HuduVudu]

I ended up with a few massive magnesium crystals growing at the bottom of the slurry.

Kewl

 

[Garf]

Kewl

Only if it was indeed magnesium crystals, perhaps it was something else, Unobtainium or something. Perhaps Mr Holmes - Farley will know

 

[Spicy Reef]

@Spicy Reef what magnesium are you using?

Seachem - Reef Advantage Magnesium

www.seachem.com

 

[Spicy Reef]

Interesting test. I’d love to see @Randy Holmes-Farley explaination. I’m guessing the calcium hydroxide has settled out, leaving a magnesium excess.

I had not thought to test calcium or specific alkalinity. From what I've read around here ph and mag are what's affected so that's all I tested... Ok, now you have me curious

 

[ZoWhat]

Kalk and Mag makes for a crispy pickle that chills you out

 

[HuduVudu]

Seachem - Reef Advantage Magnesium

www.seachem.com

Kinda defeats the purpose of using Kalk when you are using Magnesium Chloride. I would just Calcium Chloride then you don't have to worry about the pH issues.

 

[Spicy Reef]

Kinda defeats the purpose of using Kalk when you are using Magnesium Chloride. I would just Calcium Chloride then you don't have to worry about the pH issues.

how does it defeat the kalk?

 

[HuduVudu]

how does it defeat the kalk?

Kalk is CaOH. Which ends up being calcium carbonate in solution. This is a VERY basic solution and because of that there are some issues surrounding it's use. Calcium hydroxide also isn't very soluble. All of this makes Kalk semi difficult to use. For most they just use sodium bicarbonate and calcium chloride (2 part). This does not have the pH issues and is much easier to deal with when it comes to precipitate. The issue with this is that you need to dose both chemicals in balance to keep the sodium and chloride in balance. Kalk means you don't have to do that. When you add magnesium chloride you are creating a chloride imbalance and will either need to water change to maintain balance or dose sodium hydroxide. At that point then why bother with the Kalk just dose the calcium chloride and the magnesium chloride with sodium bicarbonate so that you can maintain the sodium chloride balance and not have to deal with the precipitate of Kalk.

 

[Spicy Reef]

Kalk is CaOH. Which ends up being calcium carbonate in solution. This is a VERY basic solution and because of that there are some issues surrounding it's use. Calcium hydroxide also isn't very soluble. All of this makes Kalk semi difficult to use. For most they just use sodium bicarbonate and calcium chloride (2 part). This does not have the pH issues and is much easier to deal with when it comes to precipitate. The issue with this is that you need to dose both chemicals in balance to keep the sodium and chloride in balance. Kalk means you don't have to do that. When you add magnesium chloride you are creating a chloride imbalance and will either need to water change to maintain balance or dose sodium hydroxide. At that point then why bother with the Kalk just dose the calcium chloride and the magnesium chloride with sodium bicarbonate so that you can maintain the sodium chloride balance and not have to deal with the precipitate of Kalk.

Thanks,
So in my experiment what should I test for to show that it has or has not precipitated out?

 

[HuduVudu]

Thanks,
So in my experiment what should I test for to show that it has or has not precipitated out?

Ok, where do I start.

First you need to understand how calcium hydroxide becomes calcium carbonate. I am going to try to keep this as simple as possible. The hydroxide OH- is what is called base. It's opposite H+ is called an acid. The measure of these two things in water is called pH. Specifically the amount of H+ in the water. The more acid the lower the pH. Also the more acid the less OH- base. Calcium hydroxide disassociates into Ca+2 and OH-1. This creates a very basic solution. Some amount of carbon dioxide CO2 from the atmosphere is usually disolved into the water. A portion of this wil convert to an acid called carbonic acid H+ CO3-2. There are other reactions here but will stick to the this simply and I will skip some things. This acid (carbonic acid) reacts with the kalkwasser to form calcium and carbonate in solution. You need the higher pH to help keep the calcium and carbonate in solution. If you have more carbonic acid then the pH will lower and at some point the solution will start to precipitate calcium carbonate. Soooooo adding more and more CO2 will start the precipitation process. It is important therefore that when you mix kalkwasser, you mix it in such a way that you limit the CO2 from the air from getting into the solution. This is why your powerhead mixed solution was cloudy, you were precipitating calcium carbonate. It would have been better to close the jar so that there was no open exposure to the air when you mix.

Kalkwasser will precipitate calcium carbonate in the presence of CO2. If you add the kalk and gently stir and then leave it open to the air, you will see a thin film develop on the top. This the calcium hydroxide interacting with the CO2 in the air to form a layer of calcium carbonate. If you stop exposure to the air then if you add enough calcium hydroxide, then some of the calcium hydroxide will settle out. This is because calcium hydroxide has a low solubility and only so much will go into solution. Once it has become saturated then it won't take anymore.

Calcium Chloride like Magnesium Chloride (which what you are dosing) have a high solubility and will go into solution easily. That is why they are preferred for dosing they don't have the limitations of Calcium Hydroxide. When you add MgCl to a calcium hydroxide solution a couple things are happening first the chloride is acting like a poison to the reaction that will precipitate out the magnesium. Second the pH of the solution will cause the magnesium to precipitate out in the form of magnesium hydroxide. These two factors will cause an equilibrium and will cause some amount of the magnesium hydroxide to precipitate. The reason that is magnesium hydroxide and not magnesium carbonate is because the hydroxide is less soluable than the carbonate. Adding more magnesium supplement into the solution once again changes the chloride equilibrium. Adjusting it upward and further poisoning the reaction allowing more magnesium.

I am sure there are calculations that will produce numbers that will yield amounts for precipitation etc .. but that isn't the point.

The point is that you are making calcium hydroxide and magnesium chloride with very small amounts of magnesium in solution. This isn't very useful as a supplement because you are getting the worst of both worlds and just producing a very large amount of precipitate. Now you have extra chloride, high pH and a problem with atomspheric CO2. This is just counter-productive.

The tests that you can do at home are pretty minimal. The pH will interfere with most home tests and there isn't really a way for you to easily separate the precipitates to test their powders. There isn't much to be learned here.

 

[Spicy Reef]

Ok, where do I start.

First you need to understand how calcium hydroxide becomes calcium carbonate. I am going to try to keep this as simple as possible. The hydroxide OH- is what is called base. It's opposite H+ is called an acid. The measure of these two things in water is called pH. Specifically the amount of H+ in the water. The more acid the lower the pH. Also the more acid the less OH- base. Calcium hydroxide disassociates into Ca+2 and OH-1. This creates a very basic solution. Some amount of carbon dioxide CO2 from the atmosphere is usually disolved into the water. A portion of this wil convert to an acid called carbonic acid H+ CO3-2. There are other reactions here but will stick to the this simply and I will skip some things. This acid (carbonic acid) reacts with the kalkwasser to form calcium and carbonate in solution. You need the higher pH to help keep the calcium and carbonate in solution. If you have more carbonic acid then the pH will lower and at some point the solution will start to precipitate calcium carbonate. Soooooo adding more and more CO2 will start the precipitation process. It is important therefore that when you mix kalkwasser, you mix it in such a way that you limit the CO2 from the air from getting into the solution. This is why your powerhead mixed solution was cloudy, you were precipitating calcium carbonate. It would have been better to close the jar so that there was no open exposure to the air when you mix.

Kalkwasser will precipitate calcium carbonate in the presence of CO2. If you add the kalk and gently stir and then leave it open to the air, you will see a thin film develop on the top. This the calcium hydroxide interacting with the CO2 in the air to form a layer of calcium carbonate. If you stop exposure to the air then if you add enough calcium hydroxide, then some of the calcium hydroxide will settle out. This is because calcium hydroxide has a low solubility and only so much will go into solution. Once it has become saturated then it won't take anymore.

Calcium Chloride like Magnesium Chloride (which what you are dosing) have a high solubility and will go into solution easily. That is why they are preferred for dosing they don't have the limitations of Calcium Hydroxide. When you add MgCl to a calcium hydroxide solution a couple things are happening first the chloride is acting like a poison to the reaction that will precipitate out the magnesium. Second the pH of the solution will cause the magnesium to precipitate out in the form of magnesium hydroxide. These two factors will cause an equilibrium and will cause some amount of the magnesium hydroxide to precipitate. The reason that is magnesium hydroxide and not magnesium carbonate is because the hydroxide is less soluable than the carbonate. Adding more magnesium supplement into the solution once again changes the chloride equilibrium. Adjusting it upward and further poisoning the reaction allowing more magnesium.

I am sure there are calculations that will produce numbers that will yield amounts for precipitation etc .. but that isn't the point.

The point is that you are making calcium hydroxide and magnesium chloride with very small amounts of magnesium in solution. This isn't very useful as a supplement because you are getting the worst of both worlds and just producing a very large amount of precipitate. Now you have extra chloride, high pH and a problem with atomspheric CO2. This is just counter-productive.

The tests that you can do at home are pretty minimal. The pH will interfere with most home tests and there isn't really a way for you to easily separate the precipitates to test their powders. There isn't much to be learned here.

So are you saying the mag test was false and or the PH test as well, and that there is no way for me to test the things you are saying?

 

[HuduVudu]

So are you saying the mag test was false and or the PH test as well, and that there is no way for me to test the things you are saying?

Your pH test looked correct. 13 is about what you will get for saturated kalk. When it whent down to 10 you precipitated out magnesium hydroxide.

Because of the high pH any other tests aren't likely to work well. They aren't designed for that high of pH. So no your mag test likely didn't provide accurate numbers on the kalk sample, but should have been fairly accurate on the straight magnesium chloride. Also to note those Salifert mag tests are all over the place and it is hard to get good readings. Better to use ICP if you want real numbers, and even then.

Just a quick note when you are testing do not touch the tip of the pipette into the sample. You are contaminating the fluid in the pipette which will throw off your numbers.

Not sure where you are going with this experiment. I guess it could be interesting from a "how does chemistry work" view point but as far as dosing with the result, it is as I have said counter-productive.

 

[Spicy Reef]

Your pH test looked correct. 13 is about what you will get for saturated kalk. When it whent down to 10 you precipitated out magnesium hydroxide.

Because of the high pH any other tests aren't likely to work well. They aren't designed for that high of pH. So no your mag test likely didn't provide accurate numbers on the kalk sample, but should have been fairly accurate on the straight magnesium chloride. Also to note those Salifert mag tests are all over the place and it is hard to get good readings. Better to use ICP if you want real numbers, and even then.

Just a quick note when you are testing do not touch the tip of the pipette into the sample. You are contaminating the fluid in the pipette which will throw off your numbers.

Not sure where you are going with this experiment. I guess it could be interesting from a "how does chemistry work" view point but as far as dosing with the result, it is as I have said counter-productive.

Thanks for your detailed answers
Trying to confirm my bias
Adding mag to kalk and dose with a single pump might be ok for a nano. I’ve been doing this with my 20long and water is testing out great
U’ld b surprised how sloppy u can be with testing and numbers are consistent. I use to have a fear of testing correctly because so many comments… I purchased several kits of all kinds and burned through them testing everything twice a day for two months. It’s pretty difficult for me to mess one up and yes, u can touch the sample as u described…
Cheers
Thanks again

 

[HuduVudu]

Thanks for your detailed answers
Trying to confirm my bias
Adding mag to kalk and dose with a single pump might be ok for a nano. I’ve been doing this with my 20long and water is testing out great
U’ld b surprised how sloppy u can be with testing and numbers are consistent. I use to have a fear of testing correctly because so many comments… I purchased several kits of all kinds and burned through them testing everything twice a day for two months. It’s pretty difficult for me to mess one up and yes, u can touch the sample as u described…
Cheers
Thanks again

Just remember there is no home test for sodium or chloride. So it is best to water change to keep these numbers balanced.

 

[Bada Bing]

Interesting topic. Anecdotally, I used to use Brightwells Kalk +2 (added Mg and Sr) in a Kalk stirrer but constantly got alot of precipitate in the stirrer even at low concentrations. Now I use pharma grade kalk at max concentration with very little precipitate but ya, got add Mg for maintenance.