Carbocalcium (calcium formate) and oxygen

[LadyTang2]

I read calcium formate depletes oxygen as it's used in the reaction that leads to alk. With fairly high dosing in a SPS tank would this be a significant amount of oxygen, enough that we might expect it to have other effects, what would that lead to? Or is it not a concern?

 

[Randy Holmes-Farley]

Well, we can calculate it, but that number may not give you an unambiguous answer for reasons given below. However, I would always dose organic carbon during the day for this reason.

let's suppose you dose 2.8 dKH per day. That's 1 meq/L. That also means you are dosing 1 meq/L of formate since each meq of formate provides one meq of alkalinity (see below).

The reaction is:

2HCOO- + O2 → 2OH- + 2CO2

So for 1 meq/L of formate added, you use up 0.5 meq/L of O2.

1 meq/L of O2 is 32 mg/L. Thus consumption is 16 mg/L.

That is higher than the saturation level of O2 in seawater (around 6mg/L).

So if it was added all at once and all oxidized immediately, it would be bad news. But even if added all at once, it will take time to be oxidized. I'm not sure how long.

If dosing is spread through the day, the impact will depend on how well oxygenated the water is.

 

[LadyTang2]

Well, we can calculate it, but that number may not give you an unambiguous answer for reasons given below. However, I would always dose organic carbon during the day for this reason.

let's suppose you dose 2.8 dKH per day. That's 1 meq/L. That also means you are dosing 1 meq/L of formate since each meq of formate provides one meq of alkalinity (see below).

The reaction is:

2HCOO- + O2 → 2OH- + 2CO2

So for 1 meq/L of formate added, you use up 0.5 meq/L of O2.

1 meq/L of O2 is 32 mg/L. Thus consumption is 16 mg/L.

That is higher than the saturation level of O2 in seawater (around 6mg/L).

So if it was added all at once and all oxidized immediately, it would be bad news. But even if added all at once, it will take time to be oxidized. I'm not sure how long.

If dosing is spread through the day, the impact will depend on how well oxygenated the water is.

Thanks Randy!

I see we are throwing off carbon dioxide here, is it possible to calculate/estimate how much this dose would lower PH by?

 

[LARedstickreefer]

I can add a bit of experience here: I started using Tropic Marin All for Reef about 1.5 months ago. I would dose all of it at night. Was up to 12mL of the stuff. Everything was great until I took my skimmer offline a few weeks ago.

All of my sps have lost color and suffered some stn.

I got my skimmer back online and changed my dosing to 12 times per day via a new doser and only 5mL total (my corals had greatly reduced their alk demands).

Looks like the stn has stopped. And found alk demand is starting to tick back up.

My only guess is that my pH must have dropped and stayed low long enough to cause damage. My pH meter was out of commission so I couldn’t check.

 

[Randy Holmes-Farley]

Thanks Randy!

I see we are throwing off carbon dioxide here, is it possible to calculate/estimate how much this dose would lower PH by?

yes, and I have measured it exactly, but such a calculation or measurement would assume no CO2 leaves the water, which isn’t the case.

 

[LARedstickreefer]

yes, and I have measured it exactly, but such a calculation or measurement would assume no CO2 leaves the water, which isn’t the case.

Let’s assume none leaves. What’s the worst case scenario?

I’m trying to figure out what could have caused my “happening”. My guess is a pH drop caused by this stuff and taking my skimmer offline.

 

[Randy Holmes-Farley]

Thanks Randy!

I see we are throwing off carbon dioxide here, is it possible to calculate/estimate how much this dose would lower PH by?

I realize I was confusing two threads, I was referring to dropping alk with acid And the pH drop.

this scenario is different somewhat, since what you are generating is bicarbonate, not just CO2 (the OH- and CO2 are effectively bicarbonate).

I show both of these effects in this article;

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

www.advancedaquarist.com

I show that dropping alk by 1.4 dKH lowered pH from 8.1 to 6.9.

But adding 1.4 dKH of alk with bicarbonate drops pH from 8.10 to 8.06. That is a real and expected drop, but is very small.

 

[LadyTang2]

I realize I was confusing two threads, I was referring to dropping alk with acid And the pH drop.

this scenario is different somewhat, since what you are generating is bicarbonate, not just CO2 (the OH- and CO2 are effectively bicarbonate).

I show both of these effects in this article;

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

www.advancedaquarist.com

I show that dropping alk by 1.4 dKH lowered pH from 8.1 to 6.9.

But adding 1.4 dKH of alk with bicarbonate drops pH from 8.10 to 8.06. That is a real and expected drop, but is very small.

So I'm clear, how much will/do you estimate 1.4 dkh of alk using calcium formate will lower ph by? 2HCOO- + O2 → 2OH- + 2CO2 Sorry I did not totally follow your answer

 

[LARedstickreefer]

So I'm clear, how much will/do you estimate 1.4 dkh of alk using calcium formate will lower ph by? 2HCOO- + O2 → 2OH- + 2CO2 Sorry I did not totally follow your answer

To piggyback: Would the drop be enough to even be concerned with?

I took my skimmer offline while dosing this stuff...That’s around the time that all of my troubles began.

 

[LadyTang2]

To piggyback: Would the drop be enough to even be concerned with?

I took my skimmer offline while dosing this stuff...That’s around the time that all of my troubles began.

Paraphrasing Randy here: Aeration equilibrates the water with the amount of CO2 in your home air. Whether it raises or lowers pH depends on if the tank has excessive or deficient CO2 relative to the home air.

This is a total guess LaRed but I wonder if your problem was related to a lack of aeration after shutting off the skimmer. No skimmer = less aeration = less oxygen in your case. Since this rxn requires oxygen you were likely oxygen deficient. Perhaps both less oxygen and therefore more formate ions hanging around, or just one of those, might cause some kind of issue.

Regardless of the chain of events that might cause, something that might allow you to turn off the skimmer but still aerate would be an air stone. I wonder if when you turned off the skimmer, you had added an air stone, if that would have prevented the issue.

I'll just pose my original question again: So I'm clear, how much will/do you estimate 1.4 dkh of alk using calcium formate will lower ph by?

 

[YankeeTankee]

Paraphrasing Randy here: Aeration equilibrates the water with the amount of CO2 in your home air. Whether it raises or lowers pH depends on if the tank has excessive or deficient CO2 relative to the home air.

This is a total guess LaRed but I wonder if your problem was related to a lack of aeration after shutting off the skimmer. No skimmer = less aeration = less oxygen in your case. Since this rxn requires oxygen you were likely oxygen deficient. Perhaps both less oxygen and therefore more formate ions hanging around, or just one of those, might cause some kind of issue.

Regardless of the chain of events that might cause, something that might allow you to turn off the skimmer but still aerate would be an air stone. I wonder if when you turned off the skimmer, you had added an air stone, if that would have prevented the issue.

I'll just pose my original question again: So I'm clear, how much will/do you estimate 1.4 dkh of alk using calcium formate will lower ph by?

@Randy Holmes-Farley

Aeration drives both oxygen and co2 into a closer equilibrium with home air right? Do you think an airstone would have helped?

If this rxn gives oh and co2 how much of that is converting to alk and how much stays as co2 and lowers ph. I'm basically wondering the same thing as ladytang which is how much will carbocalcium lower ph by if dosing say 1,4 dkh worth of alk.

 

[LARedstickreefer]

Also, if I’m understanding right, Carbo-Calcium reaction to alk doesn’t boost pH like a 2-Part, right?

If this is the case, and the pH drop can be significant, it would be nice for the manufacturers to warn about this in the instructions.

I took my skimmer completely offline for a week while dosing this stuff.

Nothing else changed, yet every single Acropora has stn to some extent with several completely gone and a few more likely to go next.

 

[Randy Holmes-Farley]

So I'm clear, how much will/do you estimate 1.4 dkh of alk using calcium formate will lower ph by? 2HCOO- + O2 → 2OH- + 2CO2 Sorry I did not totally follow your answer

very little. Too small for you to measure since it is very small and spread out over time allowing the tank to blow off CO2.

 

[Randy Holmes-Farley]

Also, if I’m understanding right, Carbo-Calcium reaction to alk doesn’t boost pH like a 2-Part, right?

If this is the case, and the pH drop can be significant, it would be nice for the manufacturers to warn about this in the instructions.

I took my skimmer completely offline for a week while dosing this stuff.

Nothing else changed, yet every single Acropora has stn to some extent with several completely gone and a few more likely to go next.

the effect on pH is like a two part made from bicarbonate, not carbonate it hydroxide, both of which raise pH.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley

Aeration drives both oxygen and co2 into a closer equilibrium with home air right? Do you think an airstone would have helped?

If this rxn gives oh and co2 how much of that is converting to alk and how much stays as co2 and lowers ph. I'm basically wondering the same thing as ladytang which is how much will carbocalcium lower ph by if dosing say 1,4 dkh worth of alk.

same as 1.4 dKH of bicarbonate. Very small.

 

[Randy Holmes-Farley]

To piggyback: Would the drop be enough to even be concerned with?

I took my skimmer offline while dosing this stuff...That’s around the time that all of my troubles began.

I wold keep a skimmer on for aeration in any system.

 

[LadyTang2]

I wold keep a skimmer on for aeration in any system.

Is it reasonable to add an airstone near where you're dripping calcium formate if you're dosing larger amounts? Or perhaps there are other techniques to get more oxygen in the water?

 

[Randy Holmes-Farley]

Is it reasonable to add an airstone near where you're dripping calcium formate if you're dosing larger amounts?

Aeration is often good. pH with carbocalcium is not a concern. O2 might be.

 

[LadyTang2]

Aeration is often good. pH with carbocalcium is not a concern. O2 might be.

Is there any advice you can give on how to help make sure there is ample O2 in the water? Maybe dosing to skimmer portion of sump or as others said using an air stone in section where you're dosing it?

 

[Randy Holmes-Farley]

Is there any advice you can give on how to help make sure there is ample O2 in the water? Maybe dosing to skimmer portion of sump or as others said using an air stone in section where you're dosing it?

dose during the day and use a skimmer. Dosing location is blindly to matter as it will likely mix in faster than it is metabolized.