Calcium Reactor CO2 Question

[GARRIGA]

My grasp of calcium reactors has always been to lower the PH to the melting point of the media used by introducing CO2. However, what happens if that reactor is placed down stream from a large biological filter? Would the CO2 generated during nitrification/denitrification also melt it to some degree even if the amount produced wasn't enough to bring the PH to the melting point? Since it's often recommended to run a second reactor to absorb the CO2 introduced then I'm hoping to use that concept to convert the effluent CO2 from the biological filter and in the process provide alkalinity and calcium as a byproduct.

Goal is to design a larger than normal biological filter to process all nutrients along with carbon dosing and phosphate management thereby delegating a protein skimmer to just gas exchange. Aiming for a low maintenance system.

Crazy idea or will I see a benefit? Media to be used will be coral skeletons because they have the highest melting point but that's open to debate or suggestions since that also releases phosphates. Although, latter can be mitigated.

 

[Mark Novack]

Without injecting CO2 from a CO2 source there will be no melting in the reactor. If the biofiltration created that low a Ph in the reactor then it would melt the corals and rock in the aquarium too. As far as a second chamber, while the chemistry is logical, in practice it has little effect on the effluent and no effect on the Ph of the aquarium. A CO2 scrubber on the skimmer is very effective for correcting calcium reactor Ph drop.

I use a double chamber reactor. Going to that from a single chamber changed nothing for Ph. The scrubber does all the work.

 

[Gtinnel]

I have never heard that the breakdown of waste through the nitrogen cycle creates CO2 and lowers the pH of the water. Assuming you’re right and it does, I’m confident in saying that there is no chance it will lower the pH enough to melt reactor media. Even if it does lower the pH going into the reactor it will just slightly reduce how much CO2 has to be injected into the reactor.

 

[taricha]

It's true that nitrification from ammonia to nitrite to nitrate does lower pH, and oxidation of organics does produce CO2 and lower pH as well. Unlikely that you would be able to concentrate these processes in a small enough volume of water to drop pH far enough below the dissolution pH for the coral media.
...but I can think of one version that might work a little bit.

Methanol denitrators

Id like to know if I can use a different carbon source in a methanol denitrator? How much more energy does methanol provide than say vodka? A methanol denitrator is basically a batch processor for nitrate removal. A container is filled with tank water, methanol is dosed. Its let sit for 4 hours...

www.reef2reef.com

I bet that in the small volume where methanol gets dumped for a methanol denitrator, aragonite media that was placed in there would dissolve a little bit.
Not enough to meet the Calcification demands of a reef tank, but some, I think.

 

[d2mini]

I have never heard that the breakdown of waste through the nitrogen cycle creates CO2 and lowers the pH of the water. Assuming you’re right and it does, I’m confident in saying that there is no chance it will lower the pH enough to melt reactor media. Even if it does lower the pH going into the reactor it will just slightly reduce how much CO2 has to be injected into the reactor.

This right here. ^^^^^

 

[GARRIGA]

My quest is trying to understand if CO2 by itself would melt the skeletons without lowering the PH to the melting point.
Trying to grasp if CO2 on its own has any affect.

Acid buffer reduces alkalinity by converting it to CO2. Perhaps there’s a process that reversed that.

Also know that denitrification returns alkalinity loss during nitrification but not sure if that utilizes CO2 during that process. Perhaps this is the process opposite of acid buffer.

Plants strip carbon from alkalinity in the absence of CO2.

Kalk converts CO2 and why PH rises.

Trying to fill in the gaps I have in grasping how CO2 exists in our systems. Focus is on the chemistry behind what happens inside a reactor vs how to operate a reactor. Latter I grasp. Forget I seek.

 

[GARRIGA]

Without injecting CO2 from a CO2 source there will be no melting in the reactor. If the biofiltration created that low a Ph in the reactor then it would melt the corals and rock in the aquarium too. As far as a second chamber, while the chemistry is logical, in practice it has little effect on the effluent and no effect on the Ph of the aquarium. A CO2 scrubber on the skimmer is very effective for correcting calcium reactor Ph drop.

I use a double chamber reactor. Going to that from a single chamber changed nothing for Ph. The scrubber does all the work.

Seems there is affect but this experiment starts with the effluent from the first chamber already being low. I’m trying to learn what CO2 does when PH isn’t below the melting point. Is there any scrubbing of the CO2.

 

[Mark Novack]

Above the reactive point of the media with carbonic acid its just passing water over rocks.

 

[GARRIGA]

Above the reactive point of the media with carbonic acid its just passing water over rocks.

That's what I'm seeking. Wanted to know if CO2 itself interacted with the media and got scrubbed.

 

[Randy Holmes-Farley]

It's true that nitrification from ammonia to nitrite to nitrate does lower pH, and oxidation of organics does produce CO2 and lower pH as well. Unlikely that you would be able to concentrate these processes in a small enough volume of water to drop pH far enough below the dissolution pH for the coral media.
...but I can think of one version that might work a little bit.

That is my expectation as well.

 

[Randy Holmes-Farley]

Seems there is affect but this experiment starts with the effluent from the first chamber already being low. I’m trying to learn what CO2 does when PH isn’t below the melting point. Is there any scrubbing of the CO2.

It effectively lowers the amount of carbonate present by converting it into bicarbonate, and if it drops low enough, more calcium carbonate dissolved since it is the concentration of calcium times the concentration of carbonate that determines if any can dissolve (or precipitate).

CO2 + H2O + CO3- —> 2 HCO3-

 

[GARRIGA]

It effectively lowers the amount of carbonate present by converting it into bicarbonate, and if it drops low enough, more calcium carbonate dissolved since it is the concentration of calcium times the concentration of carbonate that determines if any can dissolve (or precipitate).

CO2 + H2O + CO3- —> 2 HCO3-

Something I've been wanting to ask you on another front as it relates to CO2. Since nitrification produces acid and denitrification produces alkalies and why reducing nitrates to zero without removing it from the system such as denitrification can provide then does that remove the CO2 created during nitrification or am I just associating acidity with CO2? Chemistry not my area of expertise but I try.

 

[Randy Holmes-Farley]

There is no CO2 created during nitrification, just acid (H+).

from one of my articles:


Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

(1) NH3 + 2O2 —> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

 

[GARRIGA]

There is no CO2 created during nitrification, just acid (H+).

from one of my articles:


Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

(1) NH3 + 2O2 —> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

Would heterotrophic decomposition of organics then be the source of CO2 I'm likely lumping into nitrification.

 

[Randy Holmes-Farley]

Would heterotrophic decomposition of organics then be the source of CO2 I'm likely lumping into nitrification.

Decomposition of organics in almost any type of metabolism that happens in a reef tank certainly produces CO2.

 

[GARRIGA]

Decomposition of organics in almost any type of metabolism that happens in a reef tank certainly produces CO2.

Then that’s where I commingled the production of CO2 and was hoping that coral skeletons would scrub it even in the absence of low enough PH to melt it. I’m the end, since I’m not removing organics with mechanical filtration or skimmer then I expect CO2 to be produced and just trying to remove it by other means and refugium/algal scrubber may not be an option.

Hence why I might employ a skimmer just to gas it out since this idea won’t work but I won’t run it to remove organics. Goal is minimal maintenance as I’m not always home and wife not going help.

 

[Randy Holmes-Farley]

Yes, the CaCO3 will not remove any CO2 or acid unless it is dissolving.

A skimmer can help if the incoming air has lower CO2 than the effective level in the water.

But high CO2 is very often driven by high CO2 in the room air, so the skimmer using room air may actually be detrimental to pH if using only inside air, at least during the day when tank CO2 is lowest..

 

[GARRIGA]

Yes, the CaCO3 will not remove any CO2 or acid unless it is dissolving.

A skimmer can help if the incoming air has lower CO2 than the effective level in the water.

But high CO2 is very often driven by high CO2 in the room air, so the skimmer using room air may actually be detrimental to pH if using only inside air, at least during the day when tank CO2 is lowest..

Skimmer will be scrubbed off incoming CO2. That part is simple enough. Unfortunately, my house is air tight because of impact windows and how it was built. An ERV for tropical climates might help and being looked at as an option but not sure it will be a plausible solution.

My occupancy has varied. When at full my ph hovers around 7.6. When it’s just the two of us it’s 8.1. Why I’m trying to minimize any additional CO2 introduced during full decomposition which is the better method due to my availability to do maintenance.

Some clarification. Not installing an actual skimmer but possibly looking into setting up a chamber with micro bubbles to replicate what a skimmer does as far as gas exchange. Goal being only to provide gas air exchange beyond surface agitation in the main display. However, this might be a losing battle if my room CO2 too saturated and why I was hoping another method could actually scrub it or transform it. Chemistry not my focus but I try my best.

One other note. Since I’m trying to perform denitrification which requires heterotrophic bacteria to consume organics then I’m guessing that will also create additional CO2 as it equates with decomposition.

Ultimately, if I can’t solve my CO2 issues then FOWLER might be my only option.

As it is now post one year experiment without WC, my alkalinity is stable. Carbon dosing is now required but I don’t add any buffer. Fact is early on my alkalinity would shoot up to 14 dkh and requiring me to add acid buffer to convert it temporarily to CO2 which quickly stabilized back to average based on occupancy size. My assumption being that the coral skeletons I’m using at the beginning of the filtration process are melting as there’s no other source of buffer.

Thinking there must have been some drop in PH at the influent yet CO2 must have been scrubbed at some point or just equalizing with my room. There’s no other explanation I have for why my alkalinity would get so high. Normally it’s at 9 when nitrates remain below 20 and goes to 10 when nitrates bottom out. I’m always tinkering with my nitrates to test the affect of it rising and dropping. Not very scientific but holistically gives me an appreciation for how I can control my parameters.

 

[GARRIGA]

One other consideration. I’m going to place either a glass lid or acrylic top with the least reduction in PAR and by pumping CO2 scrubbed air plus positive pressure thereby reducing the affect of room CO2 from entering and forcing an equalization. Not sure on how I’m going to create positive air pressure yet but familiar with the process as I’ve employed that in my PC builds to minimize dust intrusion. Why Kalk may not be an option. Expecting very little evaporation

 

[GARRIGA]

It effectively lowers the amount of carbonate present by converting it into bicarbonate, and if it drops low enough, more calcium carbonate dissolved since it is the concentration of calcium times the concentration of carbonate that determines if any can dissolve (or precipitate).

CO2 + H2O + CO3- —> 2 HCO3-

There is no CO2 created during nitrification, just acid (H+).

from one of my articles:


Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

(1) NH3 + 2O2 —> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

After more digestion and my often struggles with chemistry the above is what confuses me and I know I'm being dense but please have patience as I'm trying to grasp the science.

1) Coral skeletons supposedly melt at 7.8 although I believe Reborn is marketed around 7.2. That's confusing.

2) Since nitrification contributes acid then wouldn't that on the surface of the coral skeleton not affect the surface PH and have an affect? Granted there's likely no affect to the system but I'm associating this with acid being placed on our hands and perhaps oversimplifying it and why I can't wrap my mind around the fact that acid produced via bacteria existing on the coral skeleton wouldn't have the affect I'm seeking.

Not looking to see if it's material in nature at this point and more to just understand the process. I know I'm confusing the affects of acid produced from nitrification with the affects of CO2 on PH but I don't know why.