All aquarium calculators
Every aquarium calculator on reefcalcs grouped by what kind of problem it solves. Chemistry tools default to US gallons and dKH; toggle units inside each calculator. Most work for freshwater fish tanks too — substrate, volume, heater wattage, and weight are unit-agnostic about whether the water is salty.
Water chemistry18
- BRS calculator altOpen alternative to BRS’s reef calculator. Same Randy + BRS Pharma recipes, plus AFR, Red Sea, Triton.
- All-For-Reef (AFR)Tropic Marin AFR daily dose by tank volume and dKH consumption — 1 mL per 25 L per dKH.
- Red Sea FoundationRed Sea Foundation A/B/C daily doses with the manufacturer’s per-mL ppm constants.
- Alkalinity dosingRandy Recipes, BRS Soda Ash, Tropic Marin AFR, Red Sea Foundation B, Triton Base 1.
- Calcium dosingRandy CaCl₂, BRS Pharma, Red Sea Foundation A, Triton dry.
- Magnesium dosingRandy DIY Recipe #3, BRS Pharma, Red Sea Foundation C, Triton dry, Tropic Marin Bio-Mg.
- KalkwasserSaturation mix and daily-dose by evaporation rate.
- Reef healthEight-parameter snapshot with colour-coded bands and one-click fixes.
- Water changePredict the post-change parameter for any dilution.
- Salt mixDry salt mass per brand — Instant Ocean, Reef Crystals, Red Sea, Tropic Marin, Fritz RPM.
- SalinitySG ↔ ppt ↔ mS/cm with hydrometer temperature correction.
- CO₂ / pH / alkHenderson-Hasselbalch carbonate solver. Two of three; we give you the third.
- Kalk drip ratemL/min drip matched to evaporation. Ca and alk added per day with pH-spike guard.
- GFO / phosphate doseCross-brand GFO, BRS HC, Seachem PhosGuard, and lanthanum chloride. Replacement schedules + overdose guard.
- Biopellet doseNP-reducing pellets (Vertex, NPX, TLF). Volume by tank size, 4-week ramp, reactor flow.
- Phyto dosePhytoFeast / Nanno / Brightwell. Per-dose mL, weekly total, bottle-life.
- Direct salt additionRaise salinity without a water change. Grams + ounces + cups, with daily-swing safety cap.
- Two-part imbalanceCheck whether alk + Ca dosing is in stoichiometric balance. Find the leak in your dosing.
Tank geometry7
- Aquarium volumeRectangular, cube, cylinder, hex, bow-front. Inches or cm in; gallons and litres out.
- Aquarium weightTotal filled weight plus PSI on the floor. Plan the upstairs build.
- SubstratePounds of sand or crushed coral by published CaribSea bulk densities.
- Aquarium gravelPounds of gravel for any freshwater fish tank — 1–2 in bed, exact bag count.
- Aquarium sandAragonite or silica sand by footprint and depth. SSB / DSB / bare-bottom guidance.
- Glass thicknessMinimum annealed or tempered thickness with SF=3.8. For DIY builds and sanity-checking imports.
- Sump bafflesChamber widths, bubble-trap span, baffle heights, and section gallons for a DIY sump.
System planning10
- StockingFreshwater inch-per-gallon with surface adjustment; qualitative saltwater bioload index.
- Return pump flowGPH for reef sumps by display volume, turnover target, and head loss. Inflated for elbows.
- Heater wattageBRS rule-of-thumb with insulation tier and redundant-pair recommendation.
- Chiller sizingBTU/hr heat load by equipment wattage and ambient drop. JBJ / TECO nameplate sizes.
- CO₂ scrubberSofnolime media life for skimmer-mounted CO₂ scrubbing when indoor air drops your pH.
- PAR / PPFD underwaterMQ-510 vs MQ-500 immersion factor with coral-specific PAR bands.
- Stocking (FW + SW)Three methods side-by-side — bio-load, surface area, inch-per-gallon — with temp/pH/schooling compatibility checks.
- EvaporationDaily and weekly evaporation by surface area, temp delta, humidity, cover, and air movement. Sizes the ATO reservoir.
- DLIDaily Light Integral from PAR × photoperiod, with coral and planted target bands.
- Electric billPer-device wattage × duty × your rate. Itemised monthly + annual cost.
Tools
Frequently asked questions
- What aquarium calculator should I use first?
- Start with the aquarium volume calculator — every other calculation depends on knowing your tank's true net water volume, not the sticker number. Once you have that, the substrate, heater wattage, and salt mix calculators set up the build; alkalinity, calcium, and magnesium dosing calculators handle ongoing care.
- Are these calculators free?
- Yes. Every calculator on reefcalcs is free, with no account, no email gate, and no paywalled outputs. The calculations run in your browser — there's no server math. The site is paid for by display ads and Amazon affiliate links.
- Do they work for freshwater fish tanks too?
- The geometry calculators (volume, weight, glass thickness), substrate calculators, heater wattage, and stocking calculator all work for freshwater tanks. The chemistry calculators — alkalinity, calcium, magnesium, salt mix, kalkwasser, salinity — are reef-specific because the consumption math and target ranges are reef chemistry.
- Where do the formulas come from?
- Every constant traces to a primary source: Randy Holmes-Farley's Reefkeeping / reefs.com articles for two-part dosing, Bulk Reef Supply's published mixing instructions for BRS Pharma products, Tropic Marin's Smart Info portal for All-For-Reef, Red Sea's official Foundation manual, and Triton's CoreChem documentation. Sources are linked inside each calculator and aggregated on the methodology page.
- Can I embed these on my own site?
- Yes. Every calculator has an embed-mode version at /embed/<slug> served as a minimal, no-chrome iframe-able widget with a small reefcalcs attribution at the bottom. Copy the iframe snippet from any calculator page.
- Are the calculators accurate enough for SPS corals?
- Yes — the dosing calculators use the same Randy and BRS recipes that SPS reefkeepers have used for two decades. SPS tanks should still confirm magnesium is in the 1,250–1,400 ppm band before raising calcium or alkalinity, and split corrections above 1.4 dKH or 50 ppm Ca across multiple days.
- Do I need an account to use the calculators?
- No. Calculator math doesn't need to know who you are — every input stays in your browser and there's nothing to log in to. A free account is optional and only adds saving your tank so it pre-fills calculators and syncs across devices. The calculators themselves will never be gated behind an email.
- How often is the math reviewed?
- Every page carries a 'last reviewed' date in the footer (currently 2026-09-30). Formulas are audited whenever a primary source publishes an update — for example, Randy Holmes-Farley's 2022 revision to the optimal nitrate range from 'undetectable' to 2–10 ppm.