Alk and Calcium precipating out of solution question.

[Macropora]

When does Alk and Calcium levels need to be before it starts to precipitate out of solution and your sandbed starts to cake up and there is a white film in the sump?

 

[fishman1069]

Im pretty sure it all depends on your mag levels. Calcium and carbonate ions are naturally attracted to each other. Magnesium ions act as a "bouncer" between the two until the corals have a chance to turn them into calcium carbonate. So if you have a low mag level and high alk or calc, your alk( carbonate ions) and calc will precipitate out of the water and end up caking up your sandbed. At least thats my understanding of it so far. If Im wrong please someone correct me

 

[AlohaTropics]

pH is very important. The lower the pH, the more calcium the water can hold. The higher the pH, the more precipitation will occur.


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[Macropora]

Im pretty sure it all depends on your mag levels. Calcium and carbonate ions are naturally attracted to each other. Magnesium ions act as a "bouncer" between the two until the corals have a chance to turn them into calcium carbonate. So if you have a low mag level and high alk or calc, your alk( carbonate ions) and calc will precipitate out of the water and end up caking up your sandbed. At least thats my understanding of it so far. If Im wrong please someone correct me

My magnesium is at 1650 ppm, 10- 11 dKH, and calcium 420-470 ppm. PH around 8.2 - 8.4.

 

[fishman1069]

That sounds like a good combo to me. Are you getting the white film and caked up sand?

 

[Boomer]

Macro


When does Alk and Calcium levels need to be before it starts to precipitate out of solution

It is not that easy, it is dependent on Ca++, pH and Alk mostly but also on Salinity and temp. These are often called Omega values.

My magnesium is at 1650 ppm, 10- 11 dKH, and calcium 420-470 ppm. PH around 8.2 - 8.4.

Your Mg++ is to high, get it to around 1300 ppm. Your dKH and pH are fine. I would try to keep that Ca++ below 450 ppm.





fishman

Im pretty sure it all depends on your mag levels. Calcium and carbonate ions are naturally attracted to each other.

No, it is Ca++ and Mg++ are attracted to ions that both "fit" into, as Ca++ and Mg++ are similar to each other.


Magnesium ions act as a "bouncer" between the two until the corals have a chance to turn them into calcium carbonate.

No, corals have about Zippo Mg++. Most corals are made of Aragonite and Mg++ does not fit into the crystal structure, as it does not have the right diameter to fit in.

So if you have a low mag level and high alk or calc, your alk( carbonate ions) and calc will precipitate out of the water and end up caking up your sandbed.

You have this part correct. Mg++ acts as a surface poison for the formation of Calcite, which precip's often are. Mg++ fits real nice into Calcite crystal structure, just like Sr++ fits real nice into Aragonite crystal structure. So, since the Mg++ acts as a surface poison for the formation of Calcite, more Mg+ goes into the building of the Calcite crystal structure. Thus, there is less loss of Ca++ as a precip.



Aloha

The lower the pH, the more calcium the water can hold. The higher the pH, the more precipitation will occur.

It is really not that simple but true in a general way. You need a buffer/Alk to really take it out of solution. I will add that Salinity also plays a roll. For example, in FW, at the same temp, Alk and pH there will be an increase in precip. As the Salinity drops the iS (Ionic Strength) is much less and the Activity much higher.

 

[NYreefNoob]

also what sand are u using ?

 

[Boomer]

I forgot.

Thanks Noob for the kinda reminder




before it starts to precipitate out of solution and your sandbed starts to cake up

That is usually a different issue, if you are taking about the SB Clumping-Up.

 

[fishman1069]

Thanx for the info Boomer but when I said Magnesium ions act as a "bouncer" between the two until the corals have a chance to turn them into calcium carbonate. I wasnt refering to the Mg being used by the corals. I was tryin to say that the corals use the carbonate ions and ca ions to make calcium carbonate. Is that correct?
I already knew this but thanx, Im still tryin to learn all the chemistry behind all this
"No, corals have about Zippo Mg++. Most corals are made of Aragonite and Mg++ does not fit into the crystal structure, as it does not have the right diameter to fit in."

 

[Macropora]

also what sand are u using ?

I use aragonite. Used the wrong word.

 

[Macropora]

Macro


When does Alk and Calcium levels need to be before it starts to precipitate out of solution

It is not that easy, it is dependent on Ca++, pH and Alk mostly but also on Salinity and temp. These are often called Omega values.

My magnesium is at 1650 ppm, 10- 11 dKH, and calcium 420-470 ppm. PH around 8.2 - 8.4.

Your Mg++ is to high, get it to around 1300 ppm. Your dKH and pH are fine. I would try to keep that Ca++ below 450 ppm.





fishman

Im pretty sure it all depends on your mag levels. Calcium and carbonate ions are naturally attracted to each other.

No, it is Ca++ and Mg++ are attracted to ions that both "fit" into, as Ca++ and Mg++ are similar to each other.


Magnesium ions act as a "bouncer" between the two until the corals have a chance to turn them into calcium carbonate.

No, corals have about Zippo Mg++. Most corals are made of Aragonite and Mg++ does not fit into the crystal structure, as it does not have the right diameter to fit in.

So if you have a low mag level and high alk or calc, your alk( carbonate ions) and calc will precipitate out of the water and end up caking up your sandbed.

You have this part correct. Mg++ acts as a surface poison for the formation of Calcite, which precip's often are. Mg++ fits real nice into Calcite crystal structure, just like Sr++ fits real nice into Aragonite crystal structure. So, since the Mg++ acts as a surface poison for the formation of Calcite, more Mg+ goes into the building of the Calcite crystal structure. Thus, there is less loss of Ca++ as a precip.



Aloha

The lower the pH, the more calcium the water can hold. The higher the pH, the more precipitation will occur.

It is really not that simple but true in a general way. You need a buffer/Alk to really take it out of solution. I will add that Salinity also plays a roll. For example, in FW, at the same temp, Alk and pH there will be an increase in precip. As the Salinity drops the iS (Ionic Strength) is much less and the Activity much higher.

Thanks Boomer, I like this forum alot! I'll bring down the magnesium which is causing the flaking. My temperature is at 78 degrees and the specific gravity is around 1.027. My pinpoint salinity monitor broke when I dropped it in the sump by accident. Will gradually bring it back down to 1.025. The two part left unwatch will spike the specific gravity in a small system which is a total of 170 gallons.

 

[Boomer]

Mg being used by the corals. I was tryin to say that the corals use the carbonate ions and ca ions to make calcium carbonate. Is that correct

Yes, that is correct.

 

[fishman1069]

Ok cool Thanks I just wanted to make sure I wasnt misinforming anyone.