Guide · 7 min read
The reef tank parameter log: what to track, how often, and what the numbers actually tell you
A reef tank is a chemistry set that eats its own inputs. Corals consume alkalinity and calcium every day, and the only way to know how fast is to log it. This guide covers the parameters worth tracking, a testing cadence you can actually sustain, and how to read a log for drift instead of chasing single readings.
Alkalinity (dKH)7.5 – 9.5Twice weekly (daily on a young SPS tank)
The fastest-moving number in a reef. Swings above ~0.5 dKH per day burn tissue.
Calcium (ppm)400 – 450Weekly
Moves with alkalinity. Log both together or the numbers lose meaning.
Magnesium (ppm)1250 – 1400Every 2 weeks
Low magnesium makes alkalinity and calcium impossible to hold.
Nitrate (ppm)2 – 10Weekly
Zero is not clean — it is starvation. Log the number, not "undetectable".
Phosphate (ppm)0.03 – 0.10Weekly
Track alongside nitrate; the ratio matters more than either alone.
Specific Gravity (SG)1.025 – 1.026Weekly, plus every top-off change
Log to three decimals and note the temperature you measured at.
Temperature (°F)77 – 79Daily glance, log weekly
A stable 79 beats a "perfect" 78 that dips to 75 overnight.
Consumption rate is the number nobody logs
Two alkalinity readings a few days apart, with your dosing held constant, tell you your tank's daily consumption. That single derived number is what lets you size a doser, predict a crash before a holiday, and notice when a coral colony has grown enough to change the demand curve. It only exists if the readings are dated and stored side by side — which is exactly what a log is for.
Sudden drops in consumption are an early warning: corals that stop taking up alkalinity are usually corals that have already stopped being happy, days before the color change you would have noticed by eye.
Stability beats the textbook number
A reef running at 7.8 dKH every single day is healthier than one bouncing between 8.0 and 9.2 while averaging "correct." When you review your log, look at the shape of the line, not the last data point. Lamnr's Stability Score does this automatically for pH — the same reading discipline applies to every other parameter you chart.
Five logging mistakes that make a reef log useless
- •Logging only when something looks wrong — the baseline is the whole point.
- •Recording alkalinity without the test kit or date, then comparing across two different kits.
- •Chasing a single reading with a large correction instead of confirming with a retest.
- •Dosing changes that never make it into the log, so the cause of a swing is invisible later.
- •Testing at random times of day — alkalinity and pH both swing on a photoperiod cycle.
Chart your reef parameters automatically
Log alkalinity, calcium, magnesium, nitrate, phosphate and specific gravity per tank, set your own ideal ranges, and watch the trend instead of the last reading. Free to use.
