Ca:Mg Balance Calculator

⚖️ Aquarium Ca:Mg Balance Calculator

Calculate magnesium from GH and calcium, get dosing advice, and check Ca:Mg balance for shrimp, plants, and reef tanks.

🦐 Calcium to Magnesium Ratio (for shrimp)

(use calculated or test value)
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💡 For Neocaridina shrimp ideal Ca:Mg is 2:1 to 4:1. For Caridina (crystals, bees) – 1:1 to 2:1. Outside these ranges may cause molting problems.

❓ Frequently Asked Questions (Magnesium & Shrimp)

🔹 What is the ideal magnesium level for freshwater shrimp?
For Neocaridina (cherry shrimp) – 5–15 ppm. For Caridina (crystal, bee shrimp) – 5–15 ppm as well, but they are more sensitive to fluctuations. Always keep stable.
🔹 Why is Ca:Mg ratio important for molting?
Calcium and magnesium work together for proper molting. Too much magnesium blocks calcium uptake. Ideal ratio: Neocaridina – 2:1 to 4:1 (Ca:Mg). Caridina – 1:1 to 2:1.
🔹 What is the "White Ring of Death"?
A white band around the shrimp's head indicates a failed molt. It is often caused by low calcium, incorrect Ca:Mg ratio, or unstable parameters. Read detailed article
🔹 How do I raise magnesium safely?
Use a dedicated magnesium supplement (liquid or powder). Increase gradually – no more than 10–20 ppm per day. Sudden changes cause stress and failed molts.
🔹 How does the calculator compute Mg from GH and Ca?
Formula: Mg (ppm) = (dGH × 17.848 – Ca_ppm × 2.5) / 4.1. It assumes all non‑calcium hardness comes from magnesium.
🔹 My shrimp have white ring – what should I check first?
Test calcium, magnesium, GH, KH, pH and temperature. Ensure Ca:Mg ratio is within ideal range. Also check for sudden parameter swings. More info

About this Calcium to Magnesium Calculator

This tool helps you figure out how much magnesium is in your aquarium water using just two simple tests – total hardness (dGH) and calcium (ppm). 

It also shows you the calcium-to-magnesium ratio, which is super important for shrimp, plants and coral health. If the ratio is off, your shrimp may struggle to molt properly (the “white ring of death”) and your plants will be unable to photosynthesize properly.

Quick tip:

  • Neocaridina shrimp (Cherry, etc.) do best with a Ca:Mg ratio around 2:1 to 4:1.

  • Caridina shrimp (Crystal, Bee, etc.) prefer 1:1 to 2:1.

🔍 How the calculation works

The calculator uses a standard formula:

Mg (ppm) = (dGH × 17.848 – Ca_ppm × 2.5) / 4.1

Don’t worry – you don’t have to do the math. Just enter your dGH and calcium, and the calculator does the rest.

Real‑life factors

No calculator is perfect. Water chemistry can be tricky – other minerals, temperature, pH, and even the accuracy of your test kits affect the results. Use this tool as a guideline, not an absolute truth.