Rotalbutterfly Calculation Error(?)

Deanna

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Hoping someone can shed some light on this:

Using @Zorfox's and RotalaButterfly calculators to determine my target Ca Gluconate dosing, I am finding that both calculators (which are using the same inputs) are understating resulting Ca levels by 15%.

For example, in order to achieve a GH level of ~8.4 dGH of only Ca, I would need 60ppm of Ca in one gallon of water. The calculators both state that 2.4g of Ca Gluc are needed to do this. However, when I add 2.4 grams, I get 70ppm Ca for a GH reading of 9.8 dGH. Can anyone explain this disconnect?

Tests conditions:
- Use API GH kit, but use 25ml of water, instead of 5ml, and divide results by 5 to increase precision.
- Using RODI water which is confirmed at zero TDS.
- Have tried this with varying quantities of water and varying ppm/GH targets.
- Using Bulk Supplements Ca Gluc purchased from Amazon (can find no ingredient data).
 

fablau

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It is possible that both calculators are slightly off. I can fix it if needed on rotalsbutterfly, but I’d like to have the opinion of some expert on this.

Thank you for bringing this to our attention.
 

Deanna

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Aug 23, 2018
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It is possible that both calculators are slightly off. I can fix it if needed on rotalsbutterfly, but I’d like to have the opinion of some expert on this.

Thank you for bringing this to our attention.

Thank you. I agree that it should be verified with those that know the chemistry.

I have since compared it to CaCl and CaSO4, both of which match the calculator values. So, regarding the Ca Gluc, either the calculator is off or my Ca Gluc is off. It may well be that this particular product is, somehow, not as pure as it claims to be.
 
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fablau

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Thank you. I agree that it should be verified with those that know the chemistry.

I have since compared it to CaCl and CaSO4, both of which match the calculator values. So, regarding the Ca Gluc, either the calculator is off or my Ca Gluc is off. It may well be that this particular product is, somehow, not as pure as it claims to be.

That also could be. Let me invite here a couple of people who could help.

Thanks.
 

Allwissend

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Hallo Deanna,

The rotalabutterfly.com calculator works correctly in calculations for calcium gluconate both from "result of my dose" and "dose to reach target" points. It is using the accepted values for the anhydrous form of Ca gluconate (C12H22CaO14) if that makes any difference. Checked calculations by hand to make sure.

The disconnect between what is theoretical, what is measured and what is reality may have its source in many places : material impurities, user error, measuring instrument error or test error.

All measuring instruments have a level of uncertainty , you are using 5 instruments in a row for your assumptions: TDS meter, scale, instrument for volume measuring, instrument for test volume measuring, GH test kit.
All substances/solutions have a degree of variation /impurity ( homogeneous, pure substances come at an increasingly high cost). Here 3 are used calcium gluconate, water, GH solution. One can add the other 2, calcium gluconate solution and calcium gluconate solution in the test tube as separate possibilities of introduced contamination.The calcium gluconate in the bag might have some leftover CaCO3 or other Ca-containing substances from the chemical process. GH kits vary from batch to batch in the same brand, between brands even more. Drop volume varies with the opening, angle and pressure of the bottle.
I will skip over the user errors because they can be very diverse.

I don't think anyone can say why your test results are different than expected without taking all the parts above and testing in a serious water chemistry lab. However one can imagine many small errors adding up . In the light of that, I would say 16% off target is not that bad. There are ways to reduce or determine this uncertainty but far as the calculator goes, it is correct.

screenCap-0036.jpg
 

Deanna

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Aug 23, 2018
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The rotalabutterfly.com calculator works correctly in calculations for calcium gluconate both from "result of my dose" and "dose to reach target" points. It is using the accepted values for the anhydrous form of Ca gluconate (C12H22CaO14) if that makes any difference. Checked calculations by hand to make sure.

Thanks for the in-depth verification and response, Mihai. While my results could certainly (and most likely) be based in the variety of conditions I have here at home, it just seemed odd that my test results for the CaCl and CaSO4 were exactly as predicted by the calculator, while the Ca Gluc was not. I will look into your thoughts regarding the hydrated/anhydrous possibility in the Ca Gluc I purchased and, if it is anhydrous, I'll just reduce the dosing by 15% vs. the calculated results. Would you expect the hydrated form to cause a 15% difference in weight vs the anhydrous form?

Further, your response affirms my suspicion that The Barr Report has the technically competent members to address such issues.
 
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Allwissend

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Hi Deanna,
If one calculates for anhydrous Ca gluconate and adds the monohydrate form instead, the aquarium concentration of Ca will be about 4% lower. The monohydrate form will add less Ca for the same mass.
 
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