Calcium measuring range: 300 – 498 mg/l
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Magnesium measuring range: 820 – 1800 mg/l
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Resolution calcium: 4 mg/l
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Magnesium dissolution: 20 mg/l
Along with sodium, potassium, chloride and sulfate, calcium (Ca2+) and magnesium (Mg2+) are among the main components of natural seawater. For creatures that form calcareous skeletons, such as hard corals and calcareous red algae, magnesium and, above all, calcium are important growth factors - both elements form the basic substance of the calcareous skeleton. In addition, numerous biochemical processes involving magnesium and calcium take place. The decrease in magnesium or calcium concentration due to cellular metabolism on the one hand and through skeletal incorporation on the other hand requires regular monitoring and possible re-dosing of the two ions in seawater aquariums. In this way it is possible to guarantee optimal and natural living conditions for all living beings and to avoid long-term damage.
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In natural seawater, the calcium content is 400-410 mg/l and the magnesium content is 1280-1320 mg/l and in a fixed ratio of 1:3,25 to each other. Because of chemical and biochemical interactions between calcium and magnesium, this concentration ratio should also be aimed for in seawater basins.
Note: In the first part, the calcium concentration is determined, then the magnesium concentration is determined using the same sample. In order to avoid mutual contamination, the dosing syringes with the syringe attachments may only ever be used for the same reagents!
Immerse the syringe in the liquid when drawing up. The metering syringes are always read from the piston, even if there is air between the piston and the liquid (due to the dead volume of the syringe attachment). The air bubble does not affect the test result.
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Calcium determination:
– Shake bottles before use!
– Rinse both glass cuvettes with tap water and then several times with aquarium water.
– Using the dosing syringe, fill exactly 5 ml of aquarium water into each glass cuvette. Set aside a cuvette as a comparison sample.
– Place a clean attachment on the 1 ml dosing syringe with red printing and draw reagent A up to mark 20 on the syringe (corresponds to 0,5 ml). Add the entire amount to the analysis sample.
– Close the glass cuvette with the stopper and swirl the solution briefly.
– Then mix the reagent B (powder) with the measuring spoon and add a level measuring spoon of reagent B to the glass cuvette with the sample. Swirl the cuvette gently until the powder is dissolved. The water sample turns light blue.
– Place another clean syringe attachment on the 1 ml dosing syringe with black printing and draw up 1 ml of reagent C.
– Now add reagent C from the syringe drop by drop to the water sample until the light blue solution becomes colorless*. Swirl the cuvette carefully after each drop. To better recognize the color change, use the comparison sample (the second cuvette prepared under point 3) and a white base and look into the two adjacent cuvettes from above. The dripping is stopped when the color change has ended and the analysis sample can no longer be distinguished from the comparison sample.
– The remaining amount of reagent C in the syringe gives the calcium concentration CCa in mg/l, which can be read from Table I.
Example: If the lower end of the syringe plunger is at 0,46 ml after the end of the titration, the remaining amount (VC) of reagent C is 0,46 ml. The calcium concentration of the sample corresponds to: Ca = 392 mg/l.
– Reagent C remaining in the syringe can be returned to the appropriate bottle C.
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*Note: If the solution becomes discolored when the first two drops of reagent C are added, it is recommended to repeat the determination with a reduced sample volume of 4 ml instead of 5 ml. Carry out the test exactly as described, but in point 3 with 4 ml sample per cuvette. You must multiply the value for the calcium concentration that you read in the table at the end of the determination by a factor of 1,25 to get the true calcium concentration of your sample.
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For example:
Sample volume in ml: 4 ml instead of 5 ml
Calcium concentration read: 440 mg/l
Real calcium concentration: CCa = [1,25 x 440 mg/l] = 550 mg/l
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Magnesium determination:
Place the third clean syringe attachment on the 1 ml dosing syringe with green plunger and draw up 1 ml of reagent D.
First add approx. 0,4 ml of reagent D to the water sample. The sample turns light blue again.
Now add the remaining reagent D from the syringe drop by drop to the water sample until the light blue solution becomes colorless**. Swirl the cuvette carefully after each drop. To better recognize the color change, use the comparison sample (second cuvette) and a white base again and look from above into the two cuvettes next to each other.
The remaining amount of reagent D in the syringe gives the magnesium concentration CMg in mg/l, which can be read from Table II.
Example: If the lower end of the syringe plunger is at 0,35 ml after the end of the titration, the remaining amount (VD) of reagent C is 0,35 ml. The magnesium concentration of the sample corresponds to: Mg = 1300 mg/l.
For a 4 ml sample, multiply the table value by 1,25 to get the correct magnesium content.
Reagent D remaining in the syringe can be returned to the appropriate bottle D. Rinse the glass cuvettes, dosing syringes and syringe attachments thoroughly with tap water and allow to dry until next use.
** Note: If the color change from light blue to colorless is not easy to see, we recommend taking the measurement under a bright source similar to daylight.
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Shelf life 6 months after opening. Store in a dark and cool place.