Magnesium oxide to increase PH

[lany2008]

Hi everyone，
Joined this hobby for three years now, and suffering PH problem for three years. Recently I found I could use MaO to increase PH and might be better than calcium hydroxide or Kalkwasser, because it doesn’t affect Ca and Alk. The chemical theory as below:

MgO + H2O = =Mg(OH)2

I trued this method and it really worked, so wondering if this will produce any side effects?

I used Kalkwasser before, my tank is small, and it doesn’t work very well, because my tank does not require that much of fresh water.

 

[lazycouch]

have you tried using an air pump before?

 

[lany2008]

have you tried using an air pump before?

Yes, I did, but don’t work.

 

[Randy Holmes-Farley]

Hi everyone，
Joined this hobby for three years now, and suffering PH problem for three years. Recently I found I could use MaO to increase PH and might be better than calcium hydroxide or Kalkwasser, because it doesn’t affect Ca and Alk. The chemical theory as below:

MgO + H2O = =Mg(OH)2

I trued this method and it really worked, so wondering if this will produce any side effects?

I used Kalkwasser before, my tank is small, and it doesn’t work very well, because my tank does not require that much of fresh water.

It raises alkalinity exactly the same as kalkwasser.

The obvious issues are rising magnesium, which limits what you can dose since it is so slowly depleted, and it is very insoluble so you will have to dose solids to the aquarium water.

 

[chipmunkofdoom2]

MgO + H2O = =Mg(OH)2

The hydroxide from this equation behaves exactly like the hydroxide in calcium or sodium hydroxide. From Randy's article on limewater:

OH- + CO2 => HCO3-
OH- + HCO3- => CO3-- + H2O

If you want to manage pH without raising alkalinity, there is no other way but to control CO2 in your tank and/or in your home. Having said that, the pH boost from a DIY two-part with NaOH is very powerful. An additive like this may help significantly if used routinely to supplement your alkalinity.

 

[Randy Holmes-Farley]

To make the point more general, it is not possible to add anything normal to seawater that raises pH that will not also raise alkalinity.

The only way to raise pH and not boost alkalinity is to somehow remove CO2 from the water.

 

[lany2008]

The hydroxide from this equation behaves exactly like the hydroxide in calcium or sodium hydroxide. From Randy's article on limewater:

OH- + CO2 => HCO3-
OH- + HCO3- => CO3-- + H2O

If you want to manage pH without raising alkalinity, there is no other way but to control CO2 in your tank and/or in your home. Having said that, the pH boost from a DIY two-part with NaOH is very powerful. An additive like this may help significantly if used routinely to supplement your alkalinity.

Many thanks！

 

[lany2008]

To make the point more general, it is not possible to add anything normal to seawater that raises pH that will not also raise alkalinity.

The only way to raise pH and not boost alkalinity is to somehow remove CO2 from the water.

Thank you Randy！

 

[Randy Holmes-Farley]

Thank you Randy！

You're welcome.

Happy Reefing

 

[mikst]

It raises alkalinity exactly the same as kalkwasser.

The obvious issues are rising magnesium, which limits what you can dose since it is so slowly depleted, and it is very insoluble so you will have to dose solids to the aquarium water.

Hi, I've been wondering a similar question with MgO, but was not wondering about pH with it, but more using it as a source of magnesium Dosing as opposite to MgCl2 or MgSO4 so as not to imbalance Cl2 or SO4 ion ratios .

I love the idea of kalkwasser and how it reacts in water to give us calcium and alkalinity in one nice package.

If MgO is a possibility for magnesium Dosing, but it increases alkalinity as well, that's simply something to test for and manage.

Thanks for the info.

 

[Randy Holmes-Farley]

Hi, I've been wondering a similar question with MgO, but was not wondering about pH with it, but more using it as a source of magnesium Dosing as opposite to MgCl2 or MgSO4 so as not to imbalance Cl2 or SO4 ion ratios .

I love the idea of kalkwasser and how it reacts in water to give us calcium and alkalinity in one nice package.

If MgO is a possibility for magnesium Dosing, but it increases alkalinity as well, that's simply something to test for and manage.

Thanks for the info.

Magnesium oxide and hydroxide are very poorly soluble in fresh water. Thus, you’d have to add the solids directly to tank water. It also adds so much alk that it could not be used for anything except small frequent magnesium doses. That said, one could do that if you wanted to, and could ensure the solids dissolved before interacting with delicate organisms.

 

[mikst]

Magnesium oxide and hydroxide are very poorly soluble in fresh water. Thus, you’d have to add the solids directly to tank water. It also adds so much alk that it could not be used for anything except small frequent magnesium doses. That said, one could do that if you wanted to, and could ensure the solids dissolved before interacting with delicate organisms.

Thanks, I definitely read multiple times (mostly from your posts) that trying to boost magnesium 100 or 200ppm or more with MgO or MgOH is not sustainable due to the alkalinity boost. I'm looking more for maintenance dosing. Maybe in the ATO. Or a part of weekly maintenance after testing levels.

You say it's not very soluble and to avoid contact with delicate organisms until fully dissolved. I guess that kind of precludes use in an ATO. What about having it contained in a fine mesh media cup housed near the return pump in the sump? Decent flow and no direct contact with critters until dissolved and sent thru the pump.

I understand if I were to use this with Ca(OH)2 I'd definitely need to pay attention to alkalinity, but from what I read, alkalinity is consumed pretty rapidly in a coraled tank.

Do I have a reasonable grasp on the use and (pre) cautions for MgO?

Thanks for your direct answer and all the posts you've made that I've read so far. I appreciate your efforts.

 

[Randy Holmes-Farley]

The ATO is out. Problem with the mesh media cup idea is the the locally elevated pH may make it a focus of precipitation of calcium carbonate. I’d try that in a bucket of old tank water before doing it in a reef tank.

Magnesium oxide and hydroxide are generally safe for handling. Phillips milk of magnesia is a slurry of magnesium hydroxide. Just avoid breathing dust or getting it in your eyes.