What actually differs between salts?
| Look at | Why it matters | Don’t assume |
|---|---|---|
| Alkalinity / KH | It decides how a water change shifts a tank you’re already dosing to a target | That higher KH is better for every reef |
| Calcium and magnesium | They set where your chemistry starts after a water change | That the right salt means you’ll never need to test or dose |
| The salinity table | Figures can only be compared at the same salinity and temperature | That two brands’ numbers compare directly without checking how they were mixed |
| Who it’s designed for | Fish-only, soft-coral, mixed-reef and SPS tanks have different priorities | That “marine salt” is unsuitable for any coral tank |
When a moderate salt makes sense
A salt with moderate alkalinity makes water changes easier to fit into an established tank, especially one already controlled by dosing or a calcium reactor. Red Sea Salt, for example, is listed at around 8 dKH and aimed at fish, invertebrates, soft corals and low-nutrient SPS.
When a boosted salt may suit you
A higher-alkalinity reef salt can suit a tank you deliberately run at higher alkalinity, where you want each water change to support that. Red Sea Coral Pro is listed at around 11–12 dKH at 34 ppt. That’s simply how the product is made, not a target for every tank or a guarantee of faster growth.
What no salt can replace
- Checking your RODI water and monitoring its TDS.
- Confirming salinity with a calibrated meter.
- Testing calcium, alkalinity and magnesium once your tank starts using them.
- A proper dosing plan, if water changes can’t keep up with demand.
Sources and limits
We checked the example figures against Red Sea Salt guidance, Red Sea Coral Pro guidance and the Aquaforest Reef Salt instructions. We haven’t tested any salt, or how livestock responds to it, ourselves.
THE SHORT ANSWER
Choose the salt whose tested chemistry matches your tank
Reef salt is usually sold with calcium, alkalinity and magnesium levels aimed at coral tanks, while general marine salt may have more modest chemistry and be aimed at fish-only tanks. But neither label is a standard: formulas, salinity and intended use vary by maker. A cheaper marine salt can still suit a reef if its tested chemistry matches your targets and you top up what your corals use.
Compare every salt at the same salinity and mixing conditions. Higher alkalinity or calcium isn’t automatically better; a big water change with chemistry far above your tank can cause an avoidable swing. Consistency, availability and cost per correctly mixed litre matter more than what the bucket calls itself.
STEP BY STEP
How to do it
- 01
Set your tank’s targets
Choose a stable salinity and calcium, alkalinity and magnesium ranges that suit your livestock and dosing method. Don’t plan around the highest numbers.
- 02
Compare claims fairly
Check the salinity, temperature and test method behind each salt’s calcium, alkalinity and magnesium figures.
- 03
Mix and test a batch
Follow the instructions, check the salinity, and test the key parameters before a big change or a switch of brand.
- 04
Count the correcting you’ll do
Include any extra dosing, testing or adjusting needed to bring the mix close to your tank’s levels.
YOUR SITUATION
What to do in your situation
Water changes don’t need boosted calcium and alkalinity
A consistent standard marine salt may be all you need, and cheaper.
Moderate consumption and regular water changes
Choose a balanced salt close to your tank’s current levels.
Dosing already controls your chemistry
Use a salt that fits that dosing, rather than relying on big boosts at each water change.
COMMON MISTAKES
Mistakes to avoid
Comparing at different salinities
A salt tested at 35 ppt can’t be compared directly with one tested at a lower salinity.
Assuming premium means consistent
Price and branding don’t prove that batches are consistent or that the salt suits your range.
Using water changes to correct the tank
A big change with boosted chemistry can cause a sudden swing. Correct deliberately, and test the batch first.
WORKED EXAMPLE
Switching from a high-alkalinity salt to a balanced one
A reef is kept at around 8 dKH, but new water mixes to about 12 dKH at the same salinity. Small water changes nudge alkalinity up a little, but an emergency 30% change could cause a much bigger jump than intended.
A salt closer to 8 dKH fits the existing dosing plan better. The first batch is mixed and tested, and the switch happens over normal water changes. The decision is about fitting the tank and repeatability, not about one alkalinity level being better than another.
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
Can I use marine salt in a reef tank?
Possibly, if its tested chemistry and purity suit your tank and you replace what your corals use.
Is high-alkalinity salt better for coral growth?
Not automatically. Stability, and matching your tank’s normal levels, matter more than a higher number.
Should I mix up the dry salt before using it?
Some salts can separate in transit. Follow the maker’s handling advice for your specific pack.