How to Mix Hydroponic Nutrients by Reservoir

The rule that goes above everything else

Never mix concentrates together before they're diluted.

Multi-part nutrients are formulated to be kept apart until they reach the water. Calcium in one part and sulphates or phosphates in another combine the instant they meet at full strength, forming compounds that drop straight out of solution.

What you get is a precipitate on the bottom of the tank and a feed missing exactly the nutrients you paid for — with nothing to warn you but a little cloudiness.

Add each part to the full volume of water separately, stirring it in before the next goes near it.

What this won't tell you

Target EC or ppm. Be wary of any generic source that does.

Strength depends on the crop, the cultivar, the growth stage, the light level, the temperature and the system — and the same plant wants different figures in propagation, in vegetative growth and in flower.

Your nutrient manufacturer publishes a feed chart for their own product, because the answer is specific to that formulation. That chart is the authority. This page scales their numbers to your reservoir, which is the part that's genuinely arithmetic.

Check your label's units

Dose rates come in ml per gallon and ml per litre, and a US gallon is 3.785411784 litres — so mistaking one for the other is a factor of nearly four.

This tool works in ml/gal and reports Part A rate AS ENTERED, per litre so you can compare directly with a metric bottle. If that figure looks nothing like your label, the wrong unit went in.

Worth doing every time you change product. Manufacturers aren't consistent about which they print.

Reduced strength keeps the ratio

Seedlings, cuttings and stressed plants are commonly run at a fraction of label strength, and some growers run below it generally.

Strength you are running applies your percentage to every part equally — which matters. Reducing one part and not the others changes the balance of the feed rather than its strength, and that's a different thing entirely.

What fraction to use is a judgement from your feed chart and from watching the plants.

Top-ups are where reservoirs drift

Plants take up water and dissolved nutrient at different rates.

So a reservoir topped up repeatedly with full-strength feed tends to climb in concentration, while one topped up with plain water falls. Neither drift is universal — it depends on the crop, the stage and the conditions.

The tool gives you the figures for either. An EC meter tells you which you actually needed, and it's the single most useful instrument in a hydroponic setup precisely because it turns this from a guess into a reading.

Measure properly

Nutrient doses are small relative to reservoir volume, so a splash judged by eye is a large percentage error — a few millilitres out on a dose of twenty is a tenth of your feed strength.

A cheap syringe or measuring cylinder removes the biggest single source of variation between one mix and the next. That matters because you can't diagnose a feeding problem if the feed is different every time.

Measure the water too. A tank filled by eye is not the volume printed on its side.

pH comes last

Adding concentrates moves pH, often substantially — so anything you adjust beforehand gets undone by the mixing.

Adjust after everything is dissolved and stirred. Let it settle a few minutes and re-check, since pH drifts as things fully dissolve, and check again over the following days because it moves as the plants feed.

That step isn't covered here. This tool handles quantities.