Skip to content
Goldie

Aquarium Calculators: Net Water Volume, Substrate & Salt Dosage

Instant, accurate calculators for real net tank volume (after substrate and hardscape displacement), substrate weight in kg/lbs, and therapeutic salt or Epsom salt dosing.

Measurement Units:

1. Actual Water Volume Displacement Calculator

Calculates true net water volume after subtracting substrate bed, hardscape rocks/driftwood, and top rim gap.

10%
Nominal ('Gross') Box Volume
112.0 L (29.6 US gal)
ACTUAL Net Water Volume
80.6 L / 21.3 gal
Pure Water Weight (Stand Load Check)
80.6 kg (178 lbs)
Always dose medications and water conditioners for your ACTUAL net water volume (80.6 L / 21.3 US gal) so you don't overdose your fish!

2. Aquarium Substrate Weight & Volume Calculator

Calculate how many liters, kilograms, or pounds of sand, gravel, or planted aqua soil your tank footprint requires.

Required Substrate Volume
14.0 L
Exact Substrate Weight
21.0 kg / 46.3 lbs
Shopping recommendation: You need 5 standard 5 kg (11 lb) bags (or 2 standard 9-liter aqua soil bags).

3. Aquarium Salt & Epsom Salt Dosage Calculator

Exact therapeutic dosages in grams, tablespoons, and teaspoons for stress, Ich, dropsy, and short baths.

Never use table salt containing iodine or anti-caking agents (yellow prussiate of soda / E536). Sodium chloride salt is toxic to live plants, snails, and scaleless fish/Corydoras catfish!
Aquarium Salt (Sodium Chloride, NaCl)
Exact Salt Weight
80.0 g (2.82 oz)
Household Spoons (Level)
≈ 5.3 tbsp(16 tsp)

Pond Winterization Calculator: Volume, Ice Aeration & Freezing Risk

Calculate actual pond water volume by basin profile, required winter air pump output to keep a gas-exchange hole open, and safe diffuser placement depth.

Safe Diffuser Depth Rule

Suspend the airstone strictly at 30–40 cm (12–15 inches) below the surface — NEVER on the pond bottom! Placing a diffuser on the bottom destroys thermal stratification and chills the +4°C (39°F) winter refuge layer.

✅ Safe overwintering depth (≥ 1.2 m / 4 ft): Holds a stable +4°C (39°F) thermal refuge layer at the bottom for koi and pond goldfish as long as a gas-exchange hole remains open.
Actual Pond Water Volume
11,520 L (11.5 m³ / 3,043 US gal)
Required Winter Air Pump Output
1,152 L/h (19.2 L/min / 304 GPH)

Rule of thumb: ~0.1 L/h of air per 1 L of pond water to vent toxic H₂S/CO₂ gases without supercooling

30–40 cm (12–15 in)

Frequently Asked Questions

Why is actual aquarium water volume lower than the tank's rated size?
Glass tank volume is calculated from outside dimensions. Once you subtract glass thickness, a 5 cm (2 inch) substrate bed, hardscape rocks/driftwood, and the 2–3 cm waterline gap at the top, a '100-liter' (26-gallon) tank typically holds only 75–82 liters of actual water. Always dose medications for net water volume.
How much substrate do I need for a planted aquarium?
For healthy root growth, aim for a 5 cm (2 inch) average substrate depth (3 cm in front sloping up to 7 cm in the back). Multiply tank length × width × desired depth (in cm) and divide by 1000 to get liters, then multiply by bulk density (1.6 kg/L for sand, 1.5 kg/L for gravel, or 0.95 kg/L for planted aqua soil).
How many grams are in a tablespoon of aquarium salt or Epsom salt?
One level tablespoon (15 ml) of aquarium salt or pure Epsom salt weighs approximately 15 grams (1 level teaspoon is ~5 grams). For dropsy edema, use 1 level tablespoon of pure Epsom salt (MgSO₄) per 20 liters (5 US gallons) of net water.

Related Guides & Treatment Protocols