Tools
Reef tools & calculators.
The interactive data other reef sites don’t have. Built to answer the size- and setup-specific questions forums answer badly — and Google can’t summarize away.
Return Pump Calculator
Enter your tank size, head height, and plumbing → the real flow each of 41 pumps delivers at your total dynamic head, ranked, with the math shown.
Live · FreeProtein Skimmer Size Calculator
Enter your tank volume + bioload → which skimmers actually fit once we derate the optimistic manufacturer ratings, ranked, with footprint and price.
Live · FreeReef Tank Cost Calculator
Itemized up-front cost + monthly running cost (electricity, salt, consumables) for any tank size and build tier.
Live · FreeSalt Cost-per-Gallon Calculator
Compare 12 reef salts by real cost per mixed gallon — not the box price — plus your actual monthly salt cost.
Live · FreeReef Dosing Calculator
Alk, calcium, or magnesium — the exact dose to hit your target, split safely across days, for DIY and bottled two-parts.
Live · FreeWater Change Calculator
Nitrate at 40 and want 10? The exact dilution math — one big change vs. a series of small ones, with gallons and the level after each step.
Live · FreeFlow Calculator
Your turnover target by coral type, minus what your return already delivers — then the wavemakers that close the gap, ranked by real cost.
Live · FreeTank Volume Calculator
True water volume — minus sand, rock, and air gap, plus sump — and the pounds of sand your bed depth needs. The number every dose depends on.
Live · FreeHeater Size Calculator
Wattage from your volume and real room temperature, why two heaters beat one, and the controller that catches the classic stuck-on failure.
Live · FreeReef PAR Calculator
Your real mount height and coral type → the PAR each fixture delivers at that depth, and which land in your target band. Built only on published PAR data.
Live · FreeSalinity Calculator
Convert specific gravity ↔ ppt ↔ conductivity at the 25°C reference, correct a hydrometer for temperature, and get a straight verdict on your number.
Live · FreeReef Stocking Calculator
Build a fish list and get a bioload score against your tank's real capacity — plus the minimum-tank and aggression warnings that actually sink stocking plans.
Live · FreeController Comparison
Apex vs GHL vs Hydros vs budget — every kit, price, and feature, side by side.