Troubleshooting: Water and chemistry
Why does my alkalinity keep swinging?
Alkalinity readings move by more than about 1 dKH between tests, or fall steadily despite dosing.
Last checked . How we check
What should I check first?
- Test at the same time of day each time. Red Sea asks for this because alkalinity moves through the day.
- Check the test kit is in date and run it twice on the same sample.
- Check salinity first: a 1 ppt rise from evaporation raises everything else too (Red Sea).
- Check the doser: bottle levels used against what it should have dosed.
- Test magnesium and calcium.
What is most likely causing it?
Most likely first. The order is our reading of how often the sources link each cause to this symptom.
- Dosing in one go instead of spread over the day. A spike after the dose and a fall by the next day.
- Consumption grew but dosing did not. A steady fall week on week as corals grow. Reef Builders suggests logging tests daily for a week to find consumption.
- Doser drift or failure. Bottle level does not match the schedule; worn tubing or a stuck pump (Reef Builders).
- Low magnesium or high calcium causing precipitation. Alkalinity falls while calcium is high; white crust on heaters and pumps. Red Sea links this to low magnesium.
- Kalkwasser timing. Swings that follow evaporation and top-off; pH rises sharply after top-off. BRS says the pH should never rise more than 0.2 from kalkwasser.
- Test error. Readings jump about with no pattern; old reagents or a different kit.
What should I do?
- Spread dosing across the day, in small doses into strong flow.
- Work out daily consumption: bring alkalinity to target, stop dosing, retest after a few days, and divide the drop by the days (Red Sea method).
- Correct slowly. Red Sea gives a daily maximum rise of 1.4 dKH (0.5 meq/L); stricter SPS keepers stay under about 0.5 dKH a day (typical, check).
- Raise magnesium if it is low before chasing alkalinity.
- Calibrate the doser monthly and replace worn tubing.
- Pick one target and hold it. Stability matters more than the number.
What not to do
- Raising alkalinity by several dKH in a day.
- Switching between methods or brands of supplement while you are chasing a swing.
When should I get help?
Something dying right now? Go to the emergency playbooks.
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| The right alkalinity |
| They assume different methods and corals. Pick the one that matches your method, and hold it steady. |
| What to dose by |
| Follow the method you use. For most beginners, alkalinity is the quickest and most sensitive test. |