What each test tells you
| Parameter | What it tells you | Example manual kit | Good to know |
|---|---|---|---|
| Alkalinity / KH | Whether your corals and dosing are using up the tank’s buffer | Salifert KH, about £8.29 | Usually the most useful trend to track often in a tank you dose |
| Calcium | Whether calcium use and your salt match your plan | Salifert calcium, about £12.49 | Check before changing calcium dosing, and note the unit and resolution |
| Magnesium | Whether a slower-moving level is drifting | Salifert magnesium, about £11.60 | Usually moves slowly, unless you know there’s an imbalance |
| Digital option | More repeatable, easier readings; the chemistry goal is the same | Hanna HI-REEFKIT, £504.48 inc VAT | A premium price, and reagents are still an ongoing cost |
Titration or digital?
Manual titration is cheap and lets you see the endpoint; digital checkers take the guesswork out of colour matching and make repeat readings easier. Neither is immune to mistakes in sampling, cleaning, timing or reagents. Choose the method you’ll actually repeat, not the one with the most impressive display.
Test before you dose
When you start or change two-part dosing, the Balling method or a calcium reactor, test first, make one measured adjustment, then test again after the interval your additive maker recommends. If you change calcium, alkalinity and magnesium all at once after one odd result, you won’t know what caused the next reading.
What to buy for your tank
- Low demand or mostly fish: alkalinity and calcium are enough to start, with the occasional magnesium check.
- A mixed reef using visible amounts: keep all three, but test alkalinity more often than magnesium.
- Going digital: budget for replacement reagents, and keep a manual kit as a sanity check.
Sources and limits
Red Sea lists Foundation Pro as a calcium, alkalinity and magnesium test family in its Reef Care range. Current UK examples include Salifert listings, Red Sea Foundation Pro and Hanna HI-REEFKIT. We haven’t tested how well the kits agree, or how easy the endpoints are to see, ourselves.
THE SHORT ANSWER
Track alkalinity first, then check calcium and magnesium alongside it
Alkalinity usually changes quickly enough to be the most useful everyday sign of how much your corals are using and how stable your dosing is. Calcium tends to move more slowly compared with what most tests can detect, and magnesium helps you read the balance but doesn’t need testing as often in every tank. All three depend on salinity, so check that first if the results all look unexpectedly high or low.
Choose kits whose range and endpoint are easy to read around your target levels. Using the same sample volume, drop size, mixing and endpoint reading every time matters as much as the brand. Automatic or digital testers remove some manual steps, but still need calibrating, reagents and the occasional cross-check.
STEP BY STEP
How to do it
- 01
Check salinity first
The wrong salinity shifts every concentration and can make several results look wrong at once. Confirm it with a calibrated meter.
- 02
Test alkalinity the same way every time
Test at a similar time of day, use clean syringes or cuvettes and read the endpoint the same way. That gives the clearest consumption trend.
- 03
Add calcium and magnesium for context
Test them as often as your livestock, water changes and dosing require. Don’t adjust all three after one surprising result.
- 04
Double-check before a big correction
Repeat the test, check expiry dates, and consider a reference solution or another method. Base big corrections on confirmed results.
YOUR SITUATION
What to do in your situation
Little is being used and water changes hold the levels
Test modestly, and don’t dose until you can measure consumption.
Alkalinity falls predictably between tests
Work out daily use and check calcium before choosing how to dose.
Small daily alkalinity swings matter
Test more often or automate, while keeping independent manual checks.
COMMON MISTAKES
Mistakes to avoid
Fixing the number, not the cause
Low results can come from a salinity error, a missed dose, precipitation or test technique. Find the cause before adding more.
Testing right after dosing
A local spike can give a misleading reading. Sample from the same place on a consistent schedule.
Using magnesium to fix alkalinity
Magnesium supports seawater chemistry, but adding it isn’t a general fix for unstable alkalinity.
WORKED EXAMPLE
Proving daily alkalinity use
A stable mixed reef tests 8.3 dKH on Monday and 7.9 dKH at the same time on Tuesday, with no water change or alkalinity dose in between. Repeating this shows a similar 0.4 dKH drop each day. That repeated pattern is far more useful than a single low reading.
The owner checks salinity and calcium, then works out a cautious replacement dose for their real net water volume. They split the starting dose across the day and keep testing until what goes in matches what’s used. The aim is stability, not an instant jump.
BEFORE YOU CHANGE ANYTHING
Write down where you’re starting from
Note the date, the equipment or product you’re using, how you measured and the conditions behind every important number. Say whether a volume is the tank’s label figure or your real net water; whether a flow is the box rating or what actually comes out; and, for test results, the salinity, test kit and time of day. A precise-looking number is useless once you’ve forgotten where it came from.
Change one thing at a time, and decide in advance what improvement will look like: a steady test trend, less detritus, a more stable temperature, a quieter tank or a lower running cost. One reading, or one good day, isn’t a trend, and a setting copied from someone else’s tank isn’t proof it suits yours. The free Reef Companion keeps your tests, maintenance and changes in one dated log, so you can see cause and effect.
MAKING CHANGES SAFELY
Protect your tank while you make the change
Take a baseline
Measure before you install equipment, change your chemistry or alter your routine. Take photos if placement matters, and note how your livestock behaves. Without a starting point, you can’t be sure what caused any difference later.
Start small
Begin with a cautious setting or dose, and keep a way back. Hang on to the old equipment until the new one has proved itself, keep your previous schedule, and don’t add livestock at the same time as a big lighting, flow or chemistry change.
Give it the right amount of time
Mechanical problems show up straight away; nutrient and coral responses can take days or weeks. Judge the change over a sensible period, but stop immediately if you see animals in distress, a leak, overheating or an electrical risk.
Afterwards, note the result and decide whether to keep, adjust or undo the change. If the result is unclear, go back to your last stable setup and measure better, rather than piling on another change.
SIX MONTHS ON
Check it’s still the right decision
What made sense on day one can stop working as livestock grows, the room warms up, equipment gets dirty or a routine turns out to be unrealistic. Set a reminder to review it in six months, comparing what you assumed with the reality: water volume, electricity, consumables, noise, cleaning time and test trends.
Test trends, real flow, temperature, light coverage or whatever the change was for
Is it still doing its job, with room to spare?
How often you clean it, how hard it is to reach, calibration drift and missed tasks
Can you keep this up without cutting corners?
Electricity, reagents, filters, spare parts, warranty and downtime
Would you make the same choice knowing the real cost?
If it’s working, you don’t need to replace it; the review simply gives you a reason to keep it, tune it or plan an upgrade before something fails.
KNOW THE LIMITS
When to get expert help
Get product-specific or professional help for anything involving floor loading, household electrics, unsafe plumbing, damaged glass, unexplained livestock deaths, or chemistry you can’t measure reliably. Use a qualified electrician for fixed wiring, and always follow the current safety instructions for your tank, equipment and additives. Never work around damaged cables, swollen batteries, leaking seals or equipment that keeps tripping the electrics.
Your livestock’s needs can also outweigh general equipment advice. Check adult size, behaviour, disease risk and each species’ light, flow and feeding needs with reputable care guides before you buy. This guide explains the equipment decision; it can’t guarantee the result for every animal or tank.
COMMON QUESTIONS
Frequently asked questions
Which parameter should I test most often?
In many growing reefs, alkalinity changes fastest and guides your dosing, but your schedule should suit your tank and method.
Can calcium look normal when alkalinity is low?
Yes. They’re measured at very different levels with different test resolutions, so one can show a change more clearly than the other.
Do I need to test magnesium every week?
Not always. It depends on your tank, salt, dosing and stability; test more often when tracking down a problem or changing what you add.