Reef calculators

Free, accurate tools for the saltwater reef aquarium — tank volume, alkalinity units, and water-change planning.

Tank volume

Real (net) water volume from outside dimensions, minus rock and sand displacement.

LengthWidthHeight

Units:cminchesRock & sand displacement10%

Gross volume

330 L87.2 US gal

Net water volume

297 L78.5 US gal

Net volume is what matters for dosing and stocking. Typical reef displacement is 8–15%.

Alkalinity converter

Convert between the three units reef tests report.

Value

dKH

8.00

meq/L

2.86

ppm CaCO₃

142.86

1 dKH = 0.357 meq/L = 17.86 ppm CaCO₃. Reef target is roughly 7–9 dKH, kept stable.

Water-change planner

How many water changes to dilute a parameter (e.g. nitrate) to your target.

Current valueTarget valueChange size (%)

5 changesWater changes needed

Assumes the new water has none of the parameter and a fully mixed tank.

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