Marine
Values
| Level | Situation |
|---|---|
| >7 ppm | Excellent |
| 5–7 ppm | Acceptable |
| 3–5 ppm | Stress for Many Species |
| <3 ppm | Dangerous — fish at the surface gasping for air |
What reduces O2?
- High temperature (hot water dissolves less O2)
- Excess injected CO2
- Limited surface area for gas exchange (tall, narrow aquarium)
- A lot of decomposing organic matter
- No nighttime aeration in planted areas
How to Increase O2
- Aeration (diffuser stone, air pump)
- Surface movement (adjust filter outlet)
- Lower the temperature
- For potted plants: Turn off the CO2 at night or set up nighttime ventilation
Salinity and Density (Seawater and Brackish Water)
What is it?
Salinity measures the concentration of dissolved salts. In marine aquariums, it is measured by:
- Density (refractometer): fresh water = 1.000, ocean ≈ 1.025
- ppt (parts per thousand): ocean ≈ 35 ppt
- Practical salinity (PSU/‰): standard scale
Values
| Type | Density | Salinity |
|---|---|---|
| Freshwater | 1.000 | 0 ppt |
| Slightly brackish | 1.003 – 1.008 | 5–12 ppt |
| Moderately brackish | 1.008 – 1.015 | 12–22 ppt |
| Marine FOWLR | 1.020 – 1.025 | 27–35 ppt |
| Coral reef | 1.024 – 1.026 | 33–36 ppt |
Evaporation and Salinity
Water evaporates but salt does not → salinity increases with evaporation. Always top off with fresh (not saltwater). Use an ATO (Automatic Top Off) in advanced marine aquariums.
Measuring Instruments
- Dual-scale refractometer (ATC): the most recommended, affordable, and accurate option
- Floating-needle hydrometer: inexpensive but not very accurate
- Digital refractometer: very accurate, expensive
- Electronic salinity meter: professional
Calcium and Magnesium (marine)
Target Values for Reefs
| Parameter | Optimal value |
|---|---|
| Calcium (Ca) | 380–450 ppm |
| Magnesium (Mg) | 1,200–1,400 ppm |
| Alkalinity (KH) | 8–12 °dKH |
Administration Methods (Dosage)
Balling System (2 parts):
- Part A: Calcium chloride (Ca + Cl)
- Part B: Sodium Bicarbonate (KH)
- It is taken in equal daily doses
Complete Balling System (3 parts):
- Part A: Ca
- Part B: KH/Alk
- Part C: Mg
- More precise; allows for independent adjustment
Calcium reactor (kalkwasser):
- Dissolves aragonite/limestone using CO2
- Produces water rich in Ca and KH
- Low operating cost; requires adjustment