Aquarium Dosing Calculator

Copy the dose from the bottle and enter how much water you are treating. You get the right amount for your tank, in the same unit and in milliliters, teaspoons, capfuls and drops.

Units
Use the real water in the tank, not the size on the label. For a water change, enter only the new water.
Copy this from the label, such as "per 50 gallons" or "per 200 liters".
Dose strength
Size of my bottle cap
Printed on the bottle or in the cap. Caps differ: check yours.
Dose for this water2.9 mL0.59 teaspoons
Water treated29 US gal110 L

The label dose is 5 mL for every 50 US gal (189 L). For 29 US gal (110 L) of water, use 2.9 mL (0.59 teaspoons).

For each US gallon
0.1 mL
For each 10 liters
0.26 mL
In milliliters
2.9 mL
In teaspoons
0.59 (0.2 tablespoons)
In capfuls of 5 mL
0.58
In drops
about 58 (a watery liquid, standard dropper)
  • Dose for the water really in the tank. Rocks, gravel and the gap at the top mean a tank holds 10 to 20% less than its label size.

What to work out next

Aquarium volumeFind the real water in your tankWater changeHow much new water to treatUnit converterGallons, liters, teaspoons

How to work out a dose for your tank

Almost every aquarium product gives its dose the same way: so much product for so much water. "5 mL for every 50 gallons." "One capful per 10 gallons." "1 tablet for 40 liters."

Your tank is rarely that exact size. The sum is simple, and easy to get wrong in a hurry.

Your dose = label dose × your water ÷ the water on the label

Worked example. The bottle says 5 mL for every 50 US gallons. You are treating 29 gallons.

5 × 29 ÷ 50 = 2.9 mL, which is a little over half a teaspoon.

This calculator works for any product, because it uses the dose printed on your own bottle. It does not know your product, so it cannot tell you what the dose should be. Always copy the numbers from the label in your hand. Makers change their formulas, and two bottles with similar names can be very different strengths.

Which water volume to use

Use the water that is really in the tank. A tank holds less than the size on its label, because the glass, the gap at the top, the gravel and the rocks all take up room. The real figure is usually 10 to 20% lower. Our volume calculator works it out.

For a water change, check what the label says:

  • if you treat the new water in a bucket first, enter only the new water;
  • if you pour tap water straight into the tank, many water conditioners say to dose for the whole tank. Follow the label.

If your tank has a sump, count its water too.

Milliliters, teaspoons, capfuls and drops

Measure In milliliters
1 US teaspoon 4.93 mL
1 US tablespoon 14.8 mL
1 capful Often 5 or 10 mL. Check your bottle
20 drops About 1 mL

Drops are the least exact. Their size depends on the dropper and on how thick the liquid is. For small tanks, a 1 mL syringe from a pharmacy is far better than counting drops or guessing at part of a capful.

Measuring small doses

A nano tank often needs less than 1 mL. You cannot pour that from a cap. Two things help:

  • use a 1 mL or 3 mL syringe with no needle;
  • for tablets and powders, dissolve one dose in a measured amount of tank water, then add the share you need. If one tablet treats 40 liters and you have 10, dissolve it in 100 mL and add 25 mL.

Common mistakes

  • Dosing for the label size. A "20 gallon" tank holding 16 gallons of water gets a 25% overdose.
  • Mixing up US and UK gallons. A UK gallon is a fifth bigger. Check which one your label means.
  • Reading "per 10 gallons" as "per gallon". It is the most common way to give ten times too much.
  • Using a kitchen spoon. Household spoons vary a lot. Use a measuring spoon or a syringe.
  • Doubling a medication to "make sure". More is not safer. Only go above the label dose if the label says you may.

Questions and answers

How do I calculate a dose for my aquarium?

Multiply the label dose by your water volume, then divide by the water volume on the label. For 5 mL per 50 gallons in a 29 gallon tank: 5 × 29 ÷ 50 = 2.9 mL.

How much water conditioner per gallon?

It depends on the product, because strengths differ a lot between brands. Find the dose on your bottle, enter it above, and the calculator gives the amount for one gallon and for your whole tank.

How many drops are in 1 mL?

About 20 for a watery liquid from a standard dropper. Thicker liquids and different droppers give bigger or smaller drops, so use a syringe when the dose matters.

How many mL is a capful?

Often 5 mL or 10 mL, but caps differ between bottles. The size is usually printed on the label or molded inside the cap. Enter yours above.

Should I dose for the tank size or the water volume?

For the water really in the tank. Glass, gravel, rocks and the gap at the top mean a tank holds about 10 to 20% less water than its label size.

Numbers for standard tanks

Have a standard tank? Its size, weight, heater and stocking are already worked out.

Sources

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