Nutrient mix

What this does

Pick a crop, pick what stage it's in, pick which nutrient product you're using, and enter your reservoir size. The calculator gives you the per-component dose, the EC target you should hit, and the pH target.

Three product profiles supported:

Masterblend 4-18-38 with calcium nitrate and Epsom salt. The standard DIY dry-salt three-part. Cheapest by a wide margin: roughly $0.05 per liter of mixed solution at full strength vs $0.20+ for liquid products. Worth the extra two minutes of weighing if you grow more than a couple of plants.

GH Flora Series (FloraMicro + FloraGro + FloraBloom). The most popular pre-mixed liquid trio. Ratios shift per growth stage to support the different N-P-K demands of vegetative growth vs flowering vs fruiting. More expensive but no weighing.

Generic by EC target for any other product. The calculator gives you the EC target for your crop and stage, and you mix to that number using your product's own dose chart on the bottle.

EC by crop, not by guess

Hydroponic stores often suggest one EC target for all leafy greens and another for all fruiting crops. Real targets vary a lot by species:

Spinach has nearly twice the EC of lettuce despite both being "leafy greens." A spinach plant in lettuce-EC nutes will tip-burn from calcium and magnesium deficiency. A lettuce plant in spinach-EC nutes will burn from sodium accumulation. The numbers matter.

Stage matters too. A flowering tomato gets a different N-P-K ratio than a vegetative tomato. Fruiting tomatoes get even more potassium and even less nitrogen. The calculator handles the stage shift automatically; you just pick where the plant is in its cycle.

Why pH matters and how to handle it

Hydroponic crops generally want pH 5.5-6.5. Lettuce tolerates the wider end; tomatoes and strawberries are happiest at 5.8-6.2. Outside this range, plants can't take up specific nutrients even if they're present in the right concentration. Iron deficiency in high-pH solutions is the classic example: the iron's there, the plant can't access it.

Tap water is usually 7-8.5. After mixing nutrients, pH typically drops to 5.5-6.5 on its own because most nutrient salts are mildly acidic. If it's still high, add a small amount of pH-down (phosphoric acid). If it drops too low after a few days (common in NFT systems with vigorous plants), pH-up (potassium hydroxide) brings it back. Check pH at the same time daily; it shifts with plant uptake.

A cheap pen-style pH meter is fine if you calibrate it monthly with pH 4 and pH 7 reference solutions. Without calibration, the readings drift unpredictably.

Mixing order matters more than people realize

For Masterblend and other dry-salt systems, pre-dissolve calcium nitrate separately from the rest. If you dump both into the same water at high concentration, calcium reacts with phosphate to form calcium phosphate, which is insoluble. The solution turns cloudy and the plants get neither the calcium nor the phosphate.

For GH Flora Series and other liquids that include calcium in the micro component, add FloraMicro first, then Gro, then Bloom. Same principle: calcium needs to be diluted before the phosphate hits the water.

The mixing order isn't a suggestion. Skipping it produces visibly cloudy solution that won't feed your plants. The calculator surfaces this advice for each product.

When to refresh the reservoir

Mixed nutrient solution doesn't last forever. After 1-2 weeks the nutrient ratios drift because plants take up nitrogen faster than potassium, micros faster than macros, and water faster than dissolved solids. EC rises (water gone, salts stayed), pH drifts, and specific deficiencies appear.

For small reservoirs under 50L, top up daily with plain water (or 1/4-strength nutrient solution if you're feeding heavily) and replace the whole reservoir every 1-2 weeks. For larger reservoirs, top up with 1/4-strength nutrient and replace every 2-4 weeks.

Test EC daily if you can. If it climbs steadily, dilute with plain water. If it drops steadily, your plants are eating faster than your top-ups are providing.