Product Review: Hanna Instruments Marine Magnesium Checker® HC HI783

by | Oct 25, 2022 | Equipment, Technology | 0 comments


The Hanna Instruments Marine Magnesium Checker HI783  is a great addition for any saltwater reef enthusiast.  The three primary water parameters for proper coral health are alkalinity, calcium, and magnesium.  Without proper levels of magnesium in the the system you can not achieve the correct balance between alkalinity and calcium.

Titration testing has been the primary tool for hobbyists for years. Though these tests work, they have a high level of subjectivity in reading the resulting colors accurately. Understanding the consumption rate of magnesium in a closed environment will help the hobbyist provide the required stability, and titration tests are cumbersome at best. Any way to simplify testing and provide a discrete value will allow the hobbyist to be more proactive in their dosing based on their specific bio-loads.


The Hanna Magnesium Checker is simple to use and is my “go to” reference tester to validate other test equipment. Reducing the number of reagents needed to perform a magnesium test also eliminates steps that can further introduce errors.

The instructions are clearly illustrated, with the correct amount of details. It shows how to use the syringes correctly to add the components A, Tank Sample, and B for each step.  No user color interpretation is required and the checker outputs a discrete value in parts-per-million.

Note: There is a difference in the instructions posted on the Hanna Instruments website compared to the ones provided in the kit I received (see pictures in the gallery below). The website instructions show a liquid component B versus an updated dry component B + updated Steps 6-7.  Also pay attention to the color imprinted on the syringes to identify the one used for Reagent A (Black) versus the Tank Sample (Blue)

Outdated Instructions on Website



Overall, I am pleased with this device since it feels very familiar, as it is similar to the other Hanna Checkers I currently have (Alkalinity, Calcium, & Phosphate LR). The tests may cost a little more, but if they are simpler, more consistent, and save me time they are worth it.

I will use the Magnesium Checker to compare to other test methods such as my Reef Kinetics Reefbot (using Red Sea Magnesium Pro reagent) and ICP tests. All tests will have some deviations and it is hard to really know how accurate something is without comparing to a known standard.

Personally, I prefer to keep my system’s magnesium higher than normal range. This is to combat algae and to keep me from having to worry too much about the exact value.

The Hanna Magnesium Checker is great half-way solution between manual testing and fully automated testing.

  • Ellery Wong

    Ellery is a mechanical systems engineer at a Fortune 500 technology company. He has automation experience in the automotive, appliance, printing and robotics industries as a product development professional but also has over 35 years of saltwater aquarium experience as a hobbyist. He currently maintains a 9 tank / 540 gallon SPS/LPS/Mixed systems. DIY is his forte!

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