Derived, not copied
Every dose comes from molar masses, equivalents and published equations of state — worked out from first principles rather than copied from another site's table, where an error would propagate silently.
About
Aquarium math, done properly.
AquariumToolbox exists because the chemistry of keeping a tank is settled and almost nobody presents it that way. The equations have been published for decades. What's been missing is a set of tools that apply them to your water, show their working, and tell you the truth even when the truth is "you don't need to buy anything."
Why this site exists
Ask the internet how much of something to add to your tank and you'll get three kinds of unhelpful answer. A forum thread from 2011 where four people disagree and nobody shows their arithmetic. A rule of thumb that was never true — "one inch of fish per gallon" is the famous one, but "half a cup of salt per gallon" and "25% weekly" are the same species of advice. Or a calculator on a manufacturer's site that quietly assumes you're using their product.
And nearly all of them ask for your tank size and take the number printed on the box. That number is wrong for every tank that has ever held water. Glass takes up space, substrate displaces more, rock more again, and the water stops an inch below the rim — a "75 gallon" reef with sand and rock in it holds closer to 62. Dose that as 75 and every additive you own lands about 20% strong, which is harmless for water conditioner and genuinely dangerous for copper.
That gap is the reason this site is built the way it is. You set up your tank once — measured, not guessed — and every calculator here works from the water you actually have.
Two hobbies, one set of arithmetic
Freshwater and reef keeping share the math of volume and almost nothing else. A planted-tank keeper needs CO2 from pH and KH and has no use for two-part dosing; a reefer needs alkalinity consumption tracked daily and will never open a fertilizer calculator. Most sites pick one audience, or serve both badly by mixing everything together.
Here you tell the site what kind of water you keep, and it puts your tools first — without hiding the others, because plenty of people run a reef and a planted tank and a quarantine tank at the same time. The dashboard changes shape the same way: the same tank profile underneath, the right questions on top.
Who's behind it
I'm not a marine biologist or an aquatic vet, and I'm not going to pretend to be one. I build calculation tools for a living — that's the work, and this site is that work pointed at aquarium water.
I think that's the right qualification for this particular job, and here's the honest reasoning: aquarium dosing is a math problem wearing a chemistry hat. The equations are settled and published. What goes wrong in practice isn't the science — it's arithmetic applied sloppily, a volume nobody measured, doses that ignore what else they change, and advice shaped by what the person giving it happens to sell. Those are engineering and integrity problems, and they're the ones I can actually fix.
Where genuine domain expertise is required, I lean on the people who have it and say so by name — see the sources below. And where this site would be out of its depth, it stays out: there are no species profiles here, no disease diagnosis, and no medication protocols, because a calculator can size a dose but it cannot look at your fish.
How you can trust the numbers
Not "trust us" — here's the mechanism, and you can check every part of it yourself.
One engine, no contradictions
All the calculators and the dashboard call the same calculation modules. Two tools on this site physically cannot give you different answers for the same water, because there is only one implementation of each formula.
100+ automated checks
The engine is covered by a test suite that runs on every change, pinned to published reference values — seawater density, standard conductivity, the accepted grams-per-dKH figures. If a change would alter a known-good result, the build fails before it reaches you.
The working is shown
Every result has a "show the math" panel with the actual arithmetic, in your units. You should never have to take a dose on trust — and if the reasoning looks wrong, you can see exactly where.
The sources we build on
The chemistry here isn't ours and we don't claim it. Salinity, density and conductivity come from the UNESCO 1983 equation of state and the Practical Salinity Scale — the same references oceanographers use, which is why our numbers agree with a lab meter rather than with a rule of thumb. The reef dosing figures are checked against Randy Holmes-Farley's published chemistry articles, the ones the hobby has relied on for twenty years. Evaporation uses the mass-transfer relation ASHRAE publishes for indoor pools. Floor loading is quoted against residential live-load figures from the building codes. Product strengths — salt mixes, conditioners, two-part — come off the manufacturers' own labels, cited on the page where they're used.
Our contribution is the implementation, the testing, and the writing — plus a stubborn insistence on showing the arithmetic so you're never asked to take a dose on faith. Where the hobby has consensus rather than a published figure, we say that's what it is.
Corrections are welcome — genuinely
A site whose entire promise is "the numbers are right" has to mean it, which means being easy to correct. If you find a mistake — in a calculation, a formula, a recommendation, or a fact in an article — [email protected] goes straight to a person. We'll fix it quickly and note on the page what changed and when. No defensiveness, no quiet edits.
That's not politeness. Test kits drift, salt mixes get reformulated without changing the bucket, and every hobby has edge cases that a formula doesn't cover. A correction channel that people actually use is the cheapest quality control there is.
How the site makes money
Some links to products earn a commission at no cost to you. That's the whole model — no ads that follow you around, no paid reviews, no sponsored placements, and nothing gated behind a signup. The rules are written down in the affiliate disclosure, and the important one is this: the math picks the recommendation, and we say so when the cheapest option is the right one.
The important rule either way: the math picks the recommendation. Plenty of the best answers in this hobby earn nothing at all — baking soda instead of bottled reef buffer, since it's the same compound at a tenth the price; Epsom salt from the pharmacy; a kitchen scale as the most useful thing a reefer can own; more water changes instead of an additive that promises to remove nitrate. We publish those anyway, because a site that recommends whatever pays best gets read once.
What's here, and what's coming
AquariumToolbox is new. There are 34 calculators live today. The reef tools are the deepest set so far — salinity, salt mixing, alkalinity, calcium, magnesium, and the two-part dosing tool that turns two test results into a daily dose — alongside the setup tools every tank needs: volume, weight, substrate, and the true water volume that all the dosing runs on. The freshwater and planted wings are being built now, starting with water changes and conditioner dosing, and the guides that explain the why behind each number follow close behind.
Your tank's details are remembered in your own browser so you don't retype them every visit — and they never reach us, which is the sort of thing that's easy to promise and easy to verify: it's covered in the privacy policy, which lists exactly what's stored and has a button that deletes the lot.