Refill marine calcium testing without confusing the method.
Keep your marine calcium workflow supplied with Hanna HI758-26, the 25-test reagent set containing liquid reagent A and powder reagent B. This refill measures calcium ions in saltwater—not calcium hardness as CaCO3 and not the freshwater HI937521 method. It serves the HI758 Marine Calcium Checker and the specifically documented Calcium, Marine procedures on HI83300, HI83303 and HI83399. Instruments and sample-preparation equipment are separate.
Official Hanna HI758-26 marine calcium set reference photo, showing liquid reagent A and powder reagent B. Reference lot/expiry markings are not a promise about supplied stock.
Match the refill to the complete method
HI83300, HI83303 and HI83399 each document 200–600 mg/L as Ca2+ for Calcium, Marine. The HI758 Checker manual separately specifies 200–600 ppm as Ca2+. Use the instrument’s own procedure, accuracy and controls; matching reagent codes do not make all instrument specifications interchangeable.
Two reagents for one marine assay
The method identifies HI7581 liquid Calcium Reagent A and HI7582 powder Calcium Reagent B. One determination uses 1 mL of A and one packet of B. The orderable HI758-26 pack is labeled 25 tests. Do not substitute freshwater calcium reagent or a calcium-hardness kit merely because both mention calcium.
Water quality is part of the measurement
Use calcium-free deionized or distilled water for the zero/dilution preparation. Calcium introduced by water, dirty apparatus or rinsing can bias the result high. Hanna recommends low-conductivity deionized water or pure vapor-distilled water; household RODI water is not automatically suitable. Do not rinse with calcium-containing tap water or saltwater.
The benchtop sequence at a glance
For the documented benchtop Calcium, Marine procedure, add 1 mL HI7581 reagent A to the cuvette, fill to the 10 mL mark with deionized water and invert 3–5 times. Zero this preparation. Add 0.1 mL marine sample, then one HI7582 reagent B packet. Shake vigorously for 15 seconds or until dissolved; let bubbles dissipate for 15 seconds before reading. Follow your exact instrument manual for controls and the full sequence.
Measure the small sample deliberately
The marine sample volume is 0.1 mL, introduced after zeroing the reagent-and-water preparation. Have the appropriate 0.1 mL minipipette and tips, 1 mL syringe, plastic pipette and clean cuvette available. Hanna describes this as a 100:1 analysis dilution; do not add a second dilution or calculation unless your exact procedure directs it.
Read the result on the right basis
The result is calcium ion concentration, Ca2+. It is not total hardness and is not a calcium carbonate equivalent. The three benchtop method references each specify 200–600 mg/L as Ca2+; the HI758 manual gives its range in ppm as Ca2+. Do not borrow the HI758 accuracy specification for a benchtop instrument.
Keep the optical reading clean
Let bubbles dissipate as the method directs, and keep the cuvette exterior dry and free of fingerprints before inserting it. Follow the HI758 manual if using that Checker, including its pipetting guidance and reading sequence. Verification standards are separate from the two reagents that react with the sample.
Plan a complete refill station
One order quantity supplies one 25-test reagent set, not a Checker, benchtop meter or accessory kit. Provide calcium-free deionized/distilled water and the required measuring apparatus separately. Check received lot/expiry information and consult both component US Safety Data Sheets. The linked manuals are instrument method references for proper context, not a separate reagent-set manual.
Frequently Asked Questions
What comes in the selected refill?
HI758-26 is the single verified 25-test marine calcium reagent set, with liquid HI7581 reagent A and powder HI7582 reagent B. The procedure uses 1 mL A plus one B packet per determination. Exact bottle volume is not asserted here.
Is this calcium hardness as CaCO3?
No. This is marine calcium ion concentration, Ca2+. It is neither calcium hardness as CaCO3 nor the freshwater HI937521 calcium reagent method.
Which instruments document HI758-26?
The HI758 Marine Calcium Checker and the Calcium, Marine methods on HI83300, HI83303 and HI83399. The Checker itself is not included. Follow the exact instrument manual; reagent compatibility does not transfer every range, accuracy or operating instruction.
What range applies to my instrument?
HI83300: 200–600 mg/L as Ca2+; HI83303: 200–600 mg/L as Ca2+; HI83399: 200–600 mg/L as Ca2+. HI758 separately specifies 200–600 ppm as Ca2+. Those ranges were checked in each individual instrument manual.
Can I use tap water or household RODI water?
Use calcium-free deionized or distilled water for the zero/dilution preparation. Calcium introduced by water, dirty apparatus or rinsing can bias the result high. Hanna recommends low-conductivity deionized water or pure vapor-distilled water; household RODI water is not automatically suitable. Do not rinse with calcium-containing tap water or saltwater.
How is the benchtop test prepared?
For the documented benchtop Calcium, Marine procedure, add 1 mL HI7581 reagent A to the cuvette, fill to the 10 mL mark with deionized water and invert 3–5 times. Zero this preparation. Add 0.1 mL marine sample, then one HI7582 reagent B packet. Shake vigorously for 15 seconds or until dissolved; let bubbles dissipate for 15 seconds before reading. Follow your exact instrument manual for controls and the full sequence.
Are pipettes, cuvettes or water supplied?
This is a reagent refill, not an instrument accessory kit. Supply the appropriate cuvette, stopper/cap, 1 mL syringe, plastic pipette, 0.1 mL minipipette and tips, and calcium-free deionized or distilled water separately.
Why do I need both Safety Data Sheets?
Reagent A (HI7581) and reagent B (HI7582) are different components with separate handling and safety information. Read both current US sheets and the instrument method before use, and check the lot/expiry markings on received stock.
