Free tools
Reef keeper tools
Calm, honest calculators for the questions that keep reefers up at night — starting with the water chemistry. Free, no sign-up, nothing saved to a server.
All tools
Tank volume & displacement calculator
Your tank's rated size isn't how much water it holds. Turn dimensions into gallons or litres, subtract rock and sand, and get the real water volume to dose, mix salt and stock by. The tool that feeds the rest.
Reef dosing calculator
Alkalinity, calcium or magnesium low? Tell us your water volume, your test result and your target — we'll work out the dose from the real chemistry and split it safely over as many days as it needs.
Salinity & specific-gravity converter
Specific gravity, ppt, or a hydrometer reading at the wrong temperature — the number-one measuring mistake in the hobby. Convert between them with the temperature correction most tools skip.
Reef parameter target chart
"What should my numbers be?" A clear, cited target range for every core parameter — salinity, alkalinity, calcium, magnesium, nitrate, phosphate, pH — with what to do when one drifts.
Salt-mix calculator
How much salt for a water change or a fresh batch? Enter your volume and target salinity and get the mix — plus a mixing-and-aging checklist so you never add unmixed saltwater to livestock.
Cleanup-crew calculator
Snails, hermits, a cleaner shrimp — how many for your tank, and which do which job? We'll size a balanced cleanup crew from your tank volume, honestly (overstocking a crew just starves it).
Fish compatibility checker
Will these saltwater fish get along? Check any combination for aggression, tank-size clashes and reef-safety — before you buy, not after — straight from our fact-checked care guides.
Stocking & tank-size calculator
How many fish can your tank really hold? Build a wish-list and we'll check each fish against its minimum tank and shoal size, flag every aggression clash, and give an honest read on how full the tank is.
Coral placement, light & flow guide
Where do I put this coral, and how much light does it need? Pick a coral for its PAR, flow and tank zone — or tell us about an empty spot and we'll show what fits. Soft corals to SPS, every figure cited.
Compare two species
Torn between two fish, corals or inverts? Put any two side by side — tank, water, temperament, light and flow — straight from our fact-checked care sheets, so you can choose with the facts in front of you.
Reef parameter tracker
Log salinity, alkalinity, calcium, magnesium, nitrate and phosphate over time and watch the trends — the digital version of our printable log, saved right in your browser. No account, nothing uploaded.
Saltwater cycling tracker
Cycling a new tank is a waiting game with three stages, and it's hard to tell where you are. Log your ammonia, nitrite and nitrate and we'll tell you the stage you're in — and when it's finally safe to add livestock.
Reef care scheduler
What actually needs doing, and how often? Pick your tank type — fish-only to SPS reef — for a daily, weekly, monthly and periodic routine of top-off, testing, water changes and cleaning. Print it and stick it by the tank.
Water test checker
You tested your water — now what? Enter your readings and get an instant, honest read on each: on target, a little off, or a problem, with the safe next step. Straight from our sourced parameter ranges.
Is my fish, coral or invert okay?
Something looks off? Tick what you're seeing and get possible causes and safe first steps — honest triage, never a diagnosis or a medication dose. Leads with the water; tells you when to get help.
What should I keep? quiz
Torn on where to start? Six quick questions match your tank size, experience and goals to the right fish, corals and inverts — scored against all our fact-checked species. A starting point, not a verdict.
All free, no sign-up, nothing saved. More tools as Coralkin grows.