Calcium-magnesium ratio
In marine aquariums the ratio between calcium and magnesium must be balanced. Magnesium allows calcium to remain in solution without precipitating.
Detailed explanation
In the natural sea the calcium:magnesium ratio is approximately 1:3.2 (calcium 420 mg/l, magnesium 1350 mg/l).
Magnesium has a critical role: it keeps calcium in solution. If magnesium drops too much, calcium precipitates as calcium carbonate (white deposits on pumps and glass) and it becomes impossible to maintain it at the desired level.
If calcium does not rise despite the dosage, the first thing to check is magnesium. Often raising magnesium to 1350 mg/l also solves the calcium problem.
The dosage of magnesium is done with magnesium chloride (in the Balling solution) or with commercial products (Red Sea Foundation C, Triton Core7 part 3).
Too high magnesium (above 1500 mg/l) can inhibit coral growth. Balance is the key.
Reference values by aquarium type
| Aquarium type | Recommended range |
|---|---|
| Marine (reef) | 1280 - 1400 mg/lNSW: 1350 mg/l. The Ca:Mg ratio should be approximately 1:3.2 |
How it is measured
Salifert or Hanna Checker drop test for magnesium. ICP for confirmation.
What happens when it is too low
Calcium drops. Impossible to keep the calcium stable. Dose magnesium before attempting to raise calcium.
What happens when it is too high
Possible inhibition of coral growth above 1500 mg/l.
Coralia Lab monitors this parameter with AI diagnostics. Tank Score alerts you when a value moves outside the recommended range for your aquarium.
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