Calcium formiate as a balanced one part additive?

[Svante]

Hi!

I'm new to this forum and would like to start my time here discussing some chemistry, as I know there are lots of people with knowledge on the subject here!

So, to start off:

I've been using a solution of coral skeletons dissolved in acetic acid as my only additive for quite a while now. It works beautiful but has one major drawback: The maximum dose is limited by the amount of organic carbon added to the tank. Too much and it results in zero nutrients and bad smell.

In theory, the decomposition of the formic acid salts of coral skeleton would do the same thing in regards to the alkalinity and calcium and magnesium added. However, formic acid is, as some of you might know a little toxic

Anyways. I tried it on some corals and little pods and stuff to check for effects of toxicity. NOTHING happened the first time. The pods did not react and the corals were fully expanded during the test.

The test was: 5 ml of saturated solution in one liter of tank water along with the corals and pods. It was allowed to stand for 4 hours or so. I checked the corals a few days after and could see no ill effects.

I also tested at higher concentrations, 25 ml per liter of tank water. This however resulted in the death of both coral (poccilopora sp.) and pods.

Seeing as the acute toxicity of the substance seems to be low, I would assume it is safe to dose into the tank at lower levels, especially since the decomposition of the formiate ion would probably be super fast.

So,

Would you try it?

Regards
Svante

 

[Randy Holmes-Farley]

[welcome]

I'm not sure what you mean by decomposition of the formate ion being fast.
It will serve as a source of organic carbon/energy for bacteria and they will consume it, just as they would acetate (albeit with significantly less energy per molecule). Are you thinking of some other degradation pathway?

I think this and the acetic acid version can be fine supplements (Salifert All In One is calcium acetate), but dissolving calcium carbonate into these acids usually (IME) leaves substantial residual acid. I've not tried formic, but I have tried acetic this way to make calcum acetate for supplementing. I concluded it didn't work out well.

What final pH do you get to when you use these acids?

I voted no because I prefer limewater/kalkwasser, and I prefer to control calcium/alkalinity and organic carbon additions separately, and I've not seen enough data on formate ion in reef tanks to know the risks.

 

[Svante]

Thanks for a quick reply, and happy to be on the forum!

I'm not sure what you mean by decomposition of the formate ion being fast.
It will serve as a source of organic carbon/energy for bacteria and they will consume it, just as they would acetate (albeit with significantly less energy per molecule). Are you thinking of some other degradation pathway?

I think this and the acetic acid version can be fine supplements (Salifert All In One is calcium acetate), but dissolving calcium carbonate into these acids usually (IME) leaves substantial residual acid. I've not tried formic, but I have tried acetic this way to make calcum acetate for supplementing. I concluded it didn't work out well.

What final pH do you get to when you use these acids?

I'm thinking of the normal biological degradation. And yes, the calories obtained by breaking down formiate ions would be a lot less then for acetate ions.

The trick when trying to dissolve carbonate compounds with these organic acids is that you have to heat it to skewer the equilibrium! I havent actually measured the pH for the acetic acid solution, but I've measured the produced gass volume of CO2 and got to a minimum of 95% reaction with the acetate. (about 11 liters of gass produced per 60 grams of Acetic acid)

I have not heated the solution with formic acid beacuse I'm a bit weary of the formic acid gas that is bound to slip out (dont have access to a cooler above the cooking vessel). This however I have measured the pH for and found it to be around 4-5 which is roughly the pKa of formic acid. Considering the pH of concentrated formic acid (85%) is way below zero, I would assume almost complete reaction.

Since calcium formiate precipitates during the reaction (a lot) and the remaining liquid phase has a pH about that of pKa. I would assume very high yield for this reaction, but I don't have the proper equipment to measure it at home.

The positive effects of the formiate version of the additive would be: Less released CO2 per added amount of calcium and less amount of bioavailable energy.

Regards
Svante

 

[disc1]

If the pH is about equal to the pKa then you're at the halfway point are you not? About half of your acid has reacted and about half is unreacted.

 

[Svante]

If the pH is about equal to the pKa then you're at the halfway point are you not? About half of your acid has reacted and about half is unreacted.

Correct in the sense that the aqueous concentrations of formiate and formic acids are about equal.

However because there is lots of precipitation going on of calcium formiate, it is not true that the reaction has gone only half way, since formiate is removed from solution as calcium formiate precipitates

It is likely that the residual aqueous phase would be 50/50 reacted and unreacted, however since calcium formiate has kind of bad solubility (160g/l) it is likely that no more then 320g/l of total Formiate and formic acid is in solution. Meaning that of the 820 total g/l of formic acid, only 160g/l is in the form ov formic acid, 160g/l as formiate ion, and 500g/l as calcium formiate?

This is just a rough estimate though, I don't feel like calculating the actual equilibrium ....:hmm4:

 

[Randy Holmes-Farley]

Formic acid isn't cheap (at least that I've seen), and you must be using a pretty concentrated solution. What were you using?

Perhaps you will have better success with heating, but I found that the pH never rose as high as I expected on mixing vinegar with oolitic aragonite.

I was actually hoping I could get it to be basic, but the pH remained low (5ish, IIRC) even after extended sitting with excess aragonite, and since the pH was within the range where bacteria thrive, the solution was likely not stable.

 

[Svante]

Thanks for the answers

I'm using 85% formic acid. And It's cheap if you've got the right connections, costs about 2 USD per liter, if you dont need the best lab grade

Going to try it and leave a comment later on!

 

[Randy Holmes-Farley]

OK, sounds good.

Good luck!

 

[dkeller_nc]

So dumb question - why not use a mineral acid to dissolve your coral skeletons? Hydrochloric comes to mind - it's true that it would add excess chloride over time, but I would think regular water changes would take care of that issue, as it does with 2-part additives. Hydrochloric would have the advantage of going to 100% completion, presuming that you've sufficient coral skeletons, is easy to get, and doesn't add any organic carbon.

 

[bertoni]

I think he wants a balanced additive. Using hydrochloric acid would remove any alkalinity from the result.

 

[dkeller_nc]

Perhaps I'm missing something, but I'm thinking that the identity of the particular acid would have no effect on the alkalinity of the resulting solution, provided that the end pH was the same.

However, your point is a good one. I'd think you'd have virtually no alkalinity to speak of in the resulting solution of dissolved coral skeletons regardless of whether acetic or formic acid was used - you'd just have mostly calcium acetate or calcium formiate with a little bit of strontium and magnesium.

In other words, this procedure wouldn't result in a "balanced" supplement.

 

[Randy Holmes-Farley]

If you use acetic, formic, or any other metabolizable organic acid, it will, after metabolism, provide all the alkalinity that the original coral contained.

CH3COO- (acetate) + 2 O2 → HCO3- + CO2 + H2O

or if used in denitrification:

5 CH3COO- (acetate) + 8 NO3- → 10 CO2 + 4 N2 + 13 OH- + H2O

 

[Svante]

Ok, so here are the results *drumroll*

Failure!!

Everyone that tried it got the same problem with SPS, slow decay from the base of the coral. I have no idea what causes it though. The sollution does work in the sense that it provides the abiotic essentials for coral growth, but the prevalence of STN on acropora in 4 out of 4 test cases tells me it's not viable long term.

Just wanted to let everyone know after testing a while that, while it does create the proper chemical abiotic parameters for coral growth it DOES NOT WORK!!

Off to invent the wheel again in some other field

 

[Randy Holmes-Farley]

Wow, sorry to hear that.

Thanks for reporting back.

 

[bertoni]

Yes, thanks for the report! I hope the corals all recover.

 

[MeoMat]

About the object this old thread, the calcium formiate.... now on the market appears a new product of TropicMarin, the CarboCalcium. They write on product description (on website) that is based on calcium formiate.

but STN observed here? Somebody use the CarboCalcium? Has the same effect?

The product has a maximum daily dosage, but from my calculations respect the classic balling I'm still using, is not enough to cover my tank consumption (I need twice to cover dKH variation, for example)

This dosage limit is related to the STN effect reported here?

 

[bertoni]

I haven't heard anything further on this topic.