Enrichment · Cultural Studies · Gardening and food

Mix the reservoir
to the EC you want.

Type the reservoir, your water’s EC, the target and the fertilizer label. The calculator works out what strength to mix at and how many millilitres of each part, and translates the EC into both ppm scales.

Mix the solutionWhat you get

The nutrient solution calculator

The worked example is a made-up 20-gallon classroom lettuce raft with a two-part fertilizer. Nothing you type leaves this browser.

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What you get

Enrichment · Cultural StudiesFree

What you finish with
The strength to mix at, millilitres of each part for the reservoir and a top-up, and the expected EC and ppm. It prints as a mixing card and downloads as a spreadsheet.
Who it is for
Teachers running classroom hydroponics, agriculture, biology and chemistry students, and home growers.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Cultural Studies space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Measure the source water’s EC.
  2. Look up a target EC for the crop and stage.
  3. Copy each part’s full-strength rate and the full-strength EC from the label.
  4. Measure out each part into the water separately.
  5. Check EC and pH and adjust in small steps.

Mix the solution

How the mix is worked out

EC is the measure of dissolved fertilizer.

The worked example: a 20-gallon lettuce raftEC to add1.0 mS/cm1.2 target − 0.2 tapStrength50%1.0 ÷ 2.0 at fullEach part50 mL5 mL/gal × 0.5 × 20 galCheck1.2 EC600 ppm on a 500 meterThe worked example: a 20-gallon lettuce raftEC to add1.0 mS/cm1.2 target − 0.2 tapStrength50%1.0 ÷ 2.0 at fullEach part50 mL5 mL/gal × 0.5 × 20 galCheck1.2 EC600 ppm on a 500 meter
Strength is set by the EC you still need to add, not by the label rate alone.

EC as a dial

Fertilizer salts carry electric current when dissolved, so electrical conductivity rises with how much is in the water. Over the range growers use, doubling the fertilizer roughly doubles the EC it adds. That makes EC a direct dial: subtract what the water starts with and scale the label rate to make up the rest.

Two ppm scales

Many meters show ppm, but they only measure EC and multiply. A 500-scale meter (TDS or NaCl) multiplies by 500, a 700-scale meter (KCl) by 700, so the same solution reads 600 or 840 ppm. Quoting EC avoids the confusion; the calculator shows both so you can match your meter.

Sources

  1. Resh, H. M. (2022). Hydroponic Food Production (8th ed.). CRC Press. Nutrient solutions and conductivity.
  2. Cornell University Controlled Environment Agriculture. Hydroponic lettuce handbook: nutrient solution management (cea.cals.cornell.edu).
  3. Penn State Extension. Hydroponics: nutrient solutions, EC and pH (extension.psu.edu).
  4. U.S. Geological Survey, Water Science School. Conductivity (electrical conductance) and water (usgs.gov).

The worked example is made up. Follow the fertilizer label and a crop guide for your plants. Your entries stay in this browser. Support: team@caveatacademic.com.