Keeping Alkalinity Stable in a Reef Aquarium
Alkalinity (KH) in a reef aquarium is not a number you set once and forget. It changes as the animals and other processes in your tank consume it. For us, the trend matters more than a supposedly perfect decimal place.
What an alkalinity test tells you
Carbonate hardness describes part of the water's buffering capacity and relates to the carbonate chemistry stony corals need to build their skeletons. A single reading does not show whether your dosing matches your tank. For that, you need several comparable readings and a record of what happened between them.
If you measure 7.8 °dKH one morning and 7.4 °dKH the next, that is a difference, not a complete dosing instruction. Test uncertainty, timing and a water change between readings can affect its interpretation. Repeat a surprising result. To calculate a dose afterwards, you also need the actual water volume and the product’s concentration.
Finding your tank's consumption
- Test consistently: Use the same test and, if possible, the same time of day. Follow its instructions.
- Record the readings: Note KH, time, dosing amount and water changes.
- Review the trend: If KH falls over several days despite unchanged dosing, the dose may no longer cover consumption. If it rises, check for overdosing.
- Adjust gradually: Change one thing and test again. If you change the dose, salt and test kit together, finding the cause becomes difficult.
Coralline algae and chemical precipitation can also affect KH. Base dosing on your own tank's trend, not another aquarium's numbers.
Sudden drop? Retest, then check the equipment
Repeat a surprising reading first. Is the reagent in good condition, and was the result read correctly? Then inspect the reservoir, tubing and dosing pump: is the reservoir empty, the tube kinked or the setting wrong? Check that the pump has actually delivered the solution.
Also check salinity and the water used for the last water change. A large correction after a single outlier may needlessly stress an otherwise stable tank. Follow the instructions for your dosing product; concentrations differ.
A closed coral is not an alkalinity test
A Torch coral that does not open may be reacting to flow, light, transport, tissue damage or pests. KH belongs on the checklist, but it does not explain every problem. With Torch corals, we pay particular attention to indirect flow. Our Torch coral care guide explains how to recognise a suitable position.
If tissue is visibly receding or coming loose, do not simply wait for the next reading. Photograph the coral under white light, note your readings and seek advice promptly.
A practical daily routine
After a change, test more frequently at comparable times. Once the trend is steady, adapt the testing frequency to your tank. Monitor calcium and magnesium as well, especially when changing your dosing routine.
The aim is a steady trend you can explain. Chasing a perfect decimal place helps little if the test, pump and records do not agree.
Suitable tests and further guidance
For regular alkalinity monitoring, browse the Salifert KH/ALK Test and Tropic Marin KH/Alkalinity Test Professional. You will find more options in our reef aquarium water test category. Follow the test instructions and record your results.
For broader checks, see our water parameter testing sequence. Our comparison of ICP analysis and home tests explains when laboratory analysis can add useful information.
Frequently asked questions
Which KH value is right for every coral?
There is no single universal value. Choose a reasonable range for your care system and keep it as stable as possible.
Can I correct a large deviation immediately?
Confirm the reading and find the cause first. The right correction depends on the deviation, tank volume and product. Avoid abrupt swings.
What information helps when I ask for advice?
Send us KH readings with their times, salinity, calcium, your dosing product and daily amount. A photo of the coral under neutral light also helps: info@coralprime.de.
