Hanna Instruments

Marine Magnesium Colorimeter HI783

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Magnesium is a crucial element in saltwater environments, as it allows calcium and carbonate to be bioavailable for corals and other invertebrates. Therefore, consistent and accurate testing of magnesium levels in your marine aquarium is vital to ensure a healthy and thriving system.


The HI783 Magnesium Checker HC by Hanna Instruments provides a simple, accurate, and affordable way to measure magnesium in saltwater/marine environments. Its color-coded syringes and straightforward testing strips ensure quick and hassle-free measurements, every time. With a digital read out, there is no more struggling to determine colors visually. 

  • Ideal for saltwater aquariums, marine biology, and aquaculture applications
  • Easier to use and more accurate than other chemical test kits
  • Color-coded syringes for simple and effortless testing
  • Dedicated to a single parameter
  • Simple one-button operation
  • Large LCD digital read out for added convenience
  • Auto shut-off to assure the battery wont be drained
  • Compact size for easy travel and storage



  • Range: 1,000 to 1,800 ppm Magnesium
  • Resolution: 5 ppm
  • Precision: ±5% of reading @ 77°F (25°C)
  • Light Source: LED @ 610 nm
  • Light Detector: Silicon photocell
  • Environment: 0 to 50°C (32 to 122°F); max 95% RH non-condensing. Prepared sample cuvette (sample plus reagents) must be 18 to 28 °C (64 to 82 °F).
  • Battery Type: (1) 1.5V AAA
  • Auto-off: After 10 minutes of non-use
  • Dimensions: 86 x 61 x 37.5 mm (3.4 x 2.4 x 1.5")
  • Weight: 64 g (2.3 oz.)
  • Method: Adaptation of the colorimetric EDTA method using calmagite indicator. The reaction between magnesium and the reagents causes a blue to violet tint in the sample.
  • Interferences: Calcium below 300 ppm and above 500 ppm
  • Reagent Set: HI783-25 (25 tests)
  • Calibration Set: HI783-11
  • Warranty: 1 Year


What’s Included?

  • (1x) HI783 Marine MagnesiumChecker HC 
  • (1x) Carrying case
  • (1x) Sample cuvette and (2x) caps
  • (1x) Marine Magnesium Starter Kit (reagents for 25 tests)
  • (1x) 1mL graduated syringe and tip
  • (1x) 5mL Syringe and tip with black printing
  • (1x) 5mL Syringe and tip with blue printing
  • (1x) 1.5V AAA Alkaline battery
  • (1x) Instruction manual
  • (1x) Quick reference guide
More Information
Manuals Product Manual
Quick Reference Guide
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Product Questions

Is the new version with the 3 minute countdown and powder packet instead of the liquid?
Question by: Mario on Nov 3, 2022, 9:43 PM
The Hanna Instruments Marine Magnesium Colorimter has been updated with the timer. The reagent kits are liquid https://www.bulkreefsupply.com/hi783-25-marine-magnesium-reagents-25-pack-hanna-instruments.html.
Answer by: Scott F. (BRS Staff) on Nov 9, 2022, 12:26 PM
Is this magnesium checker the new updated version? The one that comes with a 3 minute timer and powder packets that replaced the bad liquid that was used or original
Question by: Mario Lopez on Nov 2, 2022, 9:30 PM
Thanks for the question! The checkers we have are the new updated version at this time. The old ones were returned to Hanna once they made the recall and are not available any longer. Please let us know if we can help with anything else!
Answer by: Kyle Thomas (BRS Staff) on Nov 9, 2022, 11:44 AM