Question for Dr. Randy Holmes-Farley about Modifying the 2-Part Recipe

Curiousbranching

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Dear Dr. Randy Holmes-Farley,

I am currently using your 2-part recipe to supplement calcium and alkalinity in my tank. However, I’m wondering if it’s possible to modify the formula to dose calcium and KH in a 1:1 molar ratio.

From my understanding, when corals and other organisms utilize calcium and alkalinity to build their skeletons as calcium carbonate (CaCO3), the consumption occurs in a 1:1 molar ratio. Please correct me if my understanding is inaccurate.

My goal is to maintain a balanced addition of calcium and carbonate, ensuring that neither component becomes deficient over time. I understand that the current ratio is designed to match coral consumption, but I’d like to know if making this adjustment could lead to any chemical imbalances or long-term issues for the system.

I’d greatly appreciate your insights!

Best regards,
 

Randy Holmes-Farley

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If you do dose exactly calcium and carbonate 1:1 (such as kalkwasser and AFR do) calcium will slowly rise or alk will fall over time. But it is easy to do if you want.
 
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Curiousbranching

Curiousbranching

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If you do dose exactly calcium and carbonate 1:1 (such as kalkwasser and AFR do) calcium will slowly rise or alk will fall over time. But it is easy to do if you want.
I just double-checked the recipe because I’m not familiar with using cups as a unit, and I might have miscalculated the dosages. After reviewing your recipe, the correct amounts should be 132g of CaCl2·2H2O per 1L of RO water and 157g of Na2CO3 per 1L of RO water for alkalinity, not 99g per 1L as I had calculated earlier. Please correct me if my calculations are still wrong.
 
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Curiousbranching

Curiousbranching

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Before I spend time doing calculations, can I ask why you want it?
I plan to set up my doser to automatically dose calcium based on the alkalinity consumption measured by the KH Director. This approach will help me better manage the solution levels in my dosing containers. With the previous setup, the daily dosing amounts were inconsistent, leading to one container running out of solution much earlier than the others.
 

Randy Holmes-Farley

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What’s the reason for this? Could you please explain it to me so I can understand better?

Sure. Most two parts are designed for 1:1 dosing and say so.


One complexity that some designers may take into account is that pure calcium carbonate does not form in a reef tank. Some of the calcium ions are replaced by magnesium, and a much smaller number by strontium, since they look very chemically like calcium and can slip into the crystal structure in its place. The strontium incorporation is small and mostly unchanged between organisms and abiotic precipitation, but magnesium incorporationvaries substantially, from almost none in some corals to about 1/10th of the calcium mass being replaced by magnesium by coralline algae.

A consequence of this incorporation of Mg and Sr is that the amount of calcium incorporated will be less than exactly 20 ppm for each 2.8 dKH of alkalinity consumed by calcification. Reef tank consumption is about 18-20 ppm calcium and 0-2 ppm magnesium to 2.8 dKH alkalinity. Some recipes may take that difference into account and some may not. There’s nothing wrong with either way, and but to do it, one has to make assumptions about how much magnesium gets incorporated on average. The long term effects will be different with different assumptions made, and a recipe that does not take it into account at all may cause calcium to slowly rise over time if the method is used to replace all consumed alkalinity. That effect does not show up in a week or two, but will show up after many weeks to months (if not lost in the noise of ongoing water changes). Curiously, Seachem Reef Fusion claims to be 1:1 dosing but the recipe incorporates 2.46 dKH of alkalinity for each 20 ppm of calcium. I’m not sure why they elected that ratio, but it seems to contain substantially excess calcium
 
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Curiousbranching

Curiousbranching

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Thank you, the information was really helpful. I now understand the reason why, and I don’t need you to do the calculations anymore since I just saw a topic from someone else that you already confirmed. I really appreciate all your support to the community, and I’m so grateful to have you here.
 

Randy Holmes-Farley

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Thank you, the information was really helpful. I now understand the reason why, and I don’t need you to do the calculations anymore since I just saw a topic from someone else that you already confirmed. I really appreciate all your support to the community, and I’m so grateful to have you here.

You’re welcome.

Happy Reefing!
 

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