A free, printable test log for reef tanks: alkalinity, calcium, magnesium, nitrate, phosphate, salinity, pH, and temperature, with room to note what you dosed or changed. It prints on one landscape page (US Letter or A4). Trends across a few weeks tell you far more than any single test.
| Date | Time | Alk (dKH) | Ca (ppm) | Mg (ppm) | NO₃ (ppm) | PO₄ (ppm) | Salinity | pH | Temp | Dosed, changed, or noticed |
|---|---|---|---|---|---|---|---|---|---|---|
| Common target | 7–9 | 400–450 | 1,250–1,400 | 2–20 | 0.03–0.10 | 33.5–35 ppt (1.025–1.026 SG) | 7.8–8.4 | Your setpoint | ||
| My target | ||||||||||
Test at the same time of day. Change one thing at a time, then retest. Daily alkalinity use = (first reading − last reading) ÷ days between them, plus whatever you dosed per day. Free dosing, kalk, water change, and salinity calculators: coralcompass.app/tools
How to use it
- Fill in your targets first. The Common target row shows typical hobby ranges. Write the numbers you actually aim for in the My target row.
- Test at the same time of day. Alkalinity and pH drift through the light cycle, so a morning test compared with an evening one can look like a swing that isn't there.
- Log what you did, not just what you measured. Doses, water changes, new corals, and equipment changes go in the notes column.
- Read down the columns. A slow, steady drift is easy to correct. A sudden jump usually means a test error or a change you made, so retest before you dose.
Turn the log into a dose
Once you have a few alkalinity readings, work out how much your tank uses per day: (first reading − last reading) ÷ days between them, plus the daily rise your current dosing adds. Then let the calculators do the rest:
- The dosing calculator gives a one-time correction to reach your target for alkalinity, calcium, or magnesium.
- The kalkwasser calculator shows whether kalk in your top-off can cover your daily use.
- The water change calculator shows how far a change will move nitrate or phosphate.
How often to test
New or unstable tanks need more frequent tests than settled ones. As a starting point, test alkalinity 2–3 times a week in a stable tank (daily while dialing in dosing or with SPS), calcium, nitrate, and phosphate weekly, and magnesium every 2–4 weeks. Our reef testing schedule has the full table, and the test kit guide covers which kits read accurately at reef levels.
Where the target ranges come from
The Common target row matches the ranges in our guides, which explain and cite the research behind them: alkalinity, calcium, and magnesium (7–9 dKH, 400–450 ppm, 1,250–1,400 ppm), nitrate and phosphate (about 2–20 ppm and 0.03–0.1 ppm for most reefs), salinity (about 35 ppt, 1.025–1.026 SG), and reef tank pH (7.8–8.4).
FAQ
What should I write down besides test results? The date and time of each test, what you dosed, any water change and its size, new livestock, equipment changes, and anything you noticed, like coral color or polyp extension. Those notes are what let you connect a swing to its cause.
How do I work out daily alkalinity use from my log? If you are not dosing, subtract the last alkalinity reading from the first and divide by the days between them: 8.4 dKH on Monday and 7.8 dKH on Thursday is 0.6 ÷ 3 = 0.2 dKH per day. If you are dosing, add the daily rise your dose provides. Test at the same time of day, because alkalinity and pH shift over the light cycle.
Are the target ranges on the sheet right for my tank? They are common hobby targets from our guides, not rules. Softie and LPS tanks often run nutrients higher, SPS-dominant tanks lower. Fill in the My target row with what your tank does well at, and keep it stable.