Water Parameters for Beginners
Corals do not die from a bad number. They die from a number that moves. Everything below is written around that one idea.
The numbers that matter
| Parameter | Target | How often |
|---|---|---|
| Temperature | 77 to 79 F, stable | Continuous |
| Salinity | 1.025 to 1.026 specific gravity, 35 ppt | Weekly, and every top off failure |
| Alkalinity | 8.0 to 9.0 dKH | Twice a week once you keep SPS |
| Calcium | 410 to 450 ppm | Weekly |
| Magnesium | 1300 to 1400 ppm | Monthly |
| Nitrate | 2 to 10 ppm | Weekly |
| Phosphate | 0.03 to 0.10 ppm | Weekly |
Stability beats perfection
A tank sitting at 7.8 dKH every single day grows better coral than a tank that bounces between 7.5 and 9.5 chasing a target. If your alkalinity is stable and slightly off the book, leave it alone. If you must change it, move no more than 0.4 dKH per day. The classic beginner disaster is dosing a tank up two points in an afternoon and burning the tips off every acro in it.
Zero is not clean, it is starving
Nitrate and phosphate are coral food, not just waste. A tank reading 0.00 on both will show you pale tissue, no polyp extension, and eventually a cyanobacteria bloom, because the corals stopped competing for anything. Aim for a small, steady, measurable amount of each.
What to buy and what to skip
- Buy: a refractometer with calibration fluid, an alkalinity test you trust, and a second thermometer to check the first one.
- Skip at the start: strip tests, and any test kit for an element you are not dosing. Testing iodine on a two month old tank tells you nothing you can act on.
- Calibrate the refractometer with 35 ppt fluid, never with RO water alone.
Water changes
Ten to twenty percent every two weeks, mixed at least overnight, matched for temperature and salinity before it goes in. A water change is a reset for the things you cannot test, not a fix for a number you broke.
When something looks wrong
Before you dose anything, look in this order: temperature, salinity, flow to that spot, a neighbor stinging it, and only then a test kit. Most of what people treat as a chemistry problem is a placement problem.