How much nutrient for a 5-gallon bucket

Turning a label dose into millilitres.

A 5-gallon bucket is the classic size for a deep water culture or Kratky setup. The nutrient label gives a dose, but not always in the unit you need. Here is how to get from the label to the right number of millilitres.

Step 1: know your real volume

A bucket sold as 5 gallons rarely holds 5 gallons of water once you leave room for the lid and net pots. Fill it to the level you actually use, or measure how much water you pour in. The reservoir volume calculator works it out from the inside dimensions. For the rest of this guide we use a full 5 US gallons, which is 18.9 litres (5 × 3.785).

Step 2: find the dose on your label

Look for the line that matches your plants and growth stage. Doses are usually given per US gallon or per litre. If your product has several parts, there will be a dose for each.

Step 3: multiply

If the dose is per gallon, multiply by 5. If it is per litre, multiply by 18.9.

• Label says 4 ml per gallon: 4 × 5 = 20 ml in the bucket.
• Label says 2 ml per litre: 2 × 18.9 = 37.9 ml in the bucket.
• Label says 1 teaspoon per gallon: 5 teaspoons, about 25 ml (a US teaspoon is 4.93 ml).

Skip the arithmetic with the hydroponic nutrient calculator, which handles up to three parts at once and both units.

Step 4: mix in the right order

Fill the bucket with water first, then add each part one at a time, stirring between them. Never mix concentrated parts together before adding them to water, because some combinations form solids. Follow the order on your label.

Step 5: check with a meter

The label dose is a starting point. Your water, your plants and your meter decide the final answer. Measure EC (and pH) after mixing. If you are at the weak end, add a little more; if you are over, add water. Many growers begin at a quarter to a half of the label dose for young plants and increase over a few weeks.

Common mistakes

• Using a household teaspoon or cap instead of a syringe or marked cylinder. For small doses the error is large.
• Mixing up gallons and litres. A US gallon is 3.785 litres, and a UK gallon is 4.546, so check which one the label means.
• Adding nutrient for a full bucket when the bucket is only half full.

If you do overshoot, the PPM calculator tells you how much water to add to dilute it.

Estimates only: always follow your nutrient manufacturer's label and check your readings with a calibrated meter.