Aquarium calculators without the folklore.
Reef and freshwater fish tank calculators — volume, substrate, dosing, salinity, lighting. Built for both freshwater and saltwater aquariums. Every constant traced to Randy Holmes-Farley, Bulk Reef Supply, Tropic Marin, Red Sea, or Triton. Free, no accounts.
Aquarium volume
Default 0.5 in to estimate interior water volume.
All calculators
Index →Aquarium volume
Rectangular, cube, cylinder, hex, bow-front. Inches or cm in; gallons and litres out.
Aquarium weight
Total filled weight plus PSI on the floor. Plan the upstairs build.
Substrate
Pounds of sand or crushed coral by published CaribSea bulk densities.
Aquarium gravel
Pounds of gravel for any freshwater fish tank — 1–2 in bed, exact bag count.
Aquarium sand
Aragonite or silica sand by footprint and depth. SSB / DSB / bare-bottom guidance.
Glass thickness
Minimum annealed or tempered thickness with SF=3.8. For DIY builds and sanity-checking imports.
Stocking
Freshwater inch-per-gallon with surface adjustment; qualitative saltwater bioload index.
BRS calculator alt
Open 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 Foundation
Red Sea Foundation A/B/C daily doses with the manufacturer’s per-mL ppm constants.
Alkalinity dosing
Randy Recipes, BRS Soda Ash, Tropic Marin AFR, Red Sea Foundation B, Triton Base 1.
Calcium dosing
Randy CaCl₂, BRS Pharma, Red Sea Foundation A, Triton dry.
Magnesium dosing
Randy Recipe 3A, BRS Pharma, Red Sea Foundation C, Triton dry, Tropic Marin Bio-Mg.
Kalkwasser
Saturation mix and daily-dose by evaporation rate.
Reef health
Eight-parameter snapshot with colour-coded bands and one-click fixes.
Water change
Predict the post-change parameter for any dilution.
Salt mix
Dry salt mass per brand — Instant Ocean, Reef Crystals, Red Sea, Tropic Marin, Fritz RPM.
Salinity
SG ↔ ppt ↔ mS/cm with hydrometer temperature correction.
CO₂ / pH / alk
Henderson-Hasselbalch carbonate solver. Two of three; we give you the third.
Return pump flow
GPH for reef sumps by display volume, turnover target, and head loss. Inflated for elbows.
Heater wattage
BRS rule-of-thumb with insulation tier and redundant-pair recommendation.
Recently updated
- Alkalinity dosing calculator2026-05-25
- Reef Health Dashboard2026-05-25
- Kalkwasser calculator2026-05-25
- Alkalinity reference2026-05-25
- Two-part dosing explained2026-05-25
References
- Parameter index — alkalinity, calcium, magnesium, salinity, pH, NO₃, PO₄, temperature.
- Starting a reef tank — the equipment and pacing guide.
- Two-part dosing explained — the chemistry behind the calculator.
- Ideal reef parameters — what the experts actually disagree about.
- Methodology — where every number on this site comes from.