Answer these three questions
| Question | If the answer is no | If the answer is yes |
|---|---|---|
| Can you measure consumption? | Don’t automate a number you haven’t seen change | Repeat your tests at regular intervals and work out the trend |
| Can water changes keep up? | Regular water changes may be the simplest answer | Compare the cost, effort and stability of dosing instead |
| Can you keep an eye on the result? | Sort out your testing routine before buying a doser | Choose a cautious schedule, with a rule for when to stop and a date to review it |
Signs it’s too early to dose
- Your tank is new, lightly stocked or still changing week to week.
- Alkalinity and calcium sit within your salt’s intended range, with no downward trend.
- You haven’t repeated the test with clean equipment and the same method.
- The dose you’re planning comes from someone else’s tank, not your own volume and consumption.
How to prove your tank needs it
Test alkalinity and calcium at the same time of day, note your water-change dates, and avoid changing several things during the testing period. A drop between two comparable readings shows your tank is using it up; a single odd result is a reason to test again. Only use your additive maker’s calculator once you have a reliable starting number. The free Reef Companion charts your readings so the trend is easy to see.
What dosing can and can’t fix
Dosing replaces what your corals measurably use. It can’t fix poor salinity control, bad source water, a faulty test kit, weak circulation or a nutrient problem. If your tank is unstable, fix the cause first.
Sources and limits
We deliberately don’t give a one-size-fits-all “start dosing at X litres” rule. Each maker’s instructions differ in strength and safe maximums; for example, Seachem’s Reef Fusion guidance asks you to dose by water volume and not exceed its daily limit. We haven’t tested any additive or tank ourselves.
THE SHORT ANSWER
Only dose once repeated tests prove a steady shortfall
A reef tank needs dosing when its livestock uses alkalinity, calcium or another essential element faster than your water changes replace it. New tanks, soft-coral tanks and lightly stocked reefs may stay in range with water changes alone. Dosing before your tank actually needs it causes instability rather than preventing it.
Prove the need with tests taken at the same time over several days, with no water change or unrecorded dose muddying the result. Check your salinity and test method, then calculate from your real net water volume. Start below the full calculated dose, retest, and adjust based on what you see.
STEP BY STEP
How to do it
- 01
Choose the parameter and target
Set a stable target range that suits your tank, rather than aiming for the highest number printed on a salt bucket.
- 02
Measure what’s being used
Test at the same time for several days with normal feeding and lighting. Note every water change and anything you add by hand.
- 03
See whether water changes cover it
Compare your chemistry just after a water change with the drop before the next one. If it stays in range, you don’t need to automate yet.
- 04
Replace it cautiously
Use a trustworthy calculator with your net water volume, split the dose where it makes sense, and retest until what you add matches what’s used.
YOUR SITUATION
What to do in your situation
Results stay steady within what your test can detect
Don’t dose. Keep your routine and check again as livestock grows.
Water changes almost hold the target
Dosing by hand may be enough, and easier to keep track of.
Repeated alkalinity falls need frequent topping up
Use a calibrated dosing pump with safeguards, and keep testing independently.
COMMON MISTAKES
Mistakes to avoid
Dosing by the label
A bottle can’t know your water volume, starting chemistry, consumption or what else you add.
Correcting an unconfirmed result
A misread endpoint, a salinity error or an expired reagent can turn a top-up into an overdose.
Raising levels too fast
Big chemistry shifts can harm livestock, even if the final number is in a normal range.
WORKED EXAMPLE
When water changes stop holding alkalinity
A mixed reef tests 8.2 dKH just after its weekly water change, 7.9 two days later and 7.4 before the next change. The drop repeats week after week while salinity stays stable. The water change brings the number back, but leaves a big weekly swing.
A cautious daily dose can replace part of what’s being used and smooth out the swing. The owner starts below the calculated amount, splits it across the day and tests often. As corals grow and use more, the dose is recalculated from the new trend, not just turned up automatically.
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
Do soft-coral tanks need dosing?
Some don’t, if water changes keep the chemistry stable. Test your own tank rather than dosing based on the type of coral.
Can water changes replace dosing?
Yes, if their size, frequency and salt keep your parameters in range without big swings.
Which parameter shows the need to dose first?
Alkalinity often shows a useful trend quickly, but calcium, magnesium and salinity give you the context you need.