Hydroponic Nutrients Complete Guide

Plants need food. In hydroponics, you're the chef. Understanding nutrients transforms you from someone following a recipe to someone who can diagnose and solve problems. This is the complete guide to feeding your plants.

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## Quick Picks: Essential Nutrient Equipment

The honest truth: Following the bottle instructions at half strength will grow healthy plants. You don't need to understand everything in this guide immediately - but this knowledge helps when something goes wrong.

## The Basics: What Plants Actually Need

Macronutrients (needed in larger amounts):

Micronutrients (needed in trace amounts): Iron, manganese, zinc, copper, boron, molybdenum, chlorine. Quality hydroponic nutrients include all of these. Deficiencies are rare with decent nutrients but common with cheap or incomplete formulas.

## Understanding NPK Ratios

Every nutrient bottle shows three numbers like 5-5-5 or 3-1-2. These are the NPK ratio - the proportion of Nitrogen, Phosphorus, and Potassium.

Higher first number (N): Promotes leafy growth. Good for lettuce, spinach, herbs in vegetative stage.

Higher second number (P): Promotes root development and flowering. Good for fruiting plants starting to flower.

Higher third number (K): Promotes overall health and fruit development. Good for tomatoes producing fruit.

For most home herb and salad growing, balanced ratios work fine. The complexity matters more for optimising specific crops at specific stages.

## EC and TDS: Measuring Concentration

EC (Electrical Conductivity) and TDS (Total Dissolved Solids) both measure how much stuff is dissolved in your water. Higher numbers mean stronger nutrient solution.

Pure water: EC 0 / TDS 0 Tap water: EC 0.2-0.6 / TDS 100-300 (varies by area) Light feeding: EC 0.8-1.2 / TDS 400-600 Medium feeding: EC 1.2-2.0 / TDS 600-1000 Heavy feeding: EC 2.0-2.8 / TDS 1000-1400

Why this matters:

Too weak and plants grow slowly. Too strong and plants burn (brown crispy leaf tips).

Typical targets by crop:

A basic EC/TDS meter costs around £15-25 and removes all guesswork. One of the most useful tools you can buy.

## Feeding Schedules

Seedling stage (first 2-3 weeks): Quarter to half strength nutrients. Delicate roots burn easily. EC around 0.4-0.8.

Vegetative growth (until flowering): Full strength as plants establish. Higher nitrogen. EC as per crop targets.

Flowering and fruiting: Shift toward phosphorus and potassium. Reduce nitrogen slightly. Same or slightly higher EC.

General principle: Start weak, increase gradually, watch plant response.

## Changing Your Reservoir

Nutrients deplete unevenly. Plants take what they need, leaving imbalances. Even if EC stays constant, the nutrient ratio changes.

Full system change: Every 1-2 weeks for recirculating systems. Empty, rinse, refill with fresh solution.

Kratky systems: Usually one fill per grow cycle for lettuce and herbs. Larger plants may need careful topping up.

Top-up practice: Between changes, add plain water (not more nutrients) to maintain level. Why? Plants drink more water than nutrients in hot weather, concentrating the solution. Adding more nutrients worsens this.

## What to Avoid

Overfeeding: The most common beginner mistake. More nutrients doesn't mean more growth. Start at half strength and increase only if plants look pale or slow.

Mixing brands: Different brands use different formulations. Mixing can cause imbalances or precipitation. Pick one brand and stick with it.

Using soil fertiliser: Miracle-Gro and similar aren't formulated for hydroponics. They lack micronutrients and can leave residues. Use proper hydroponic nutrients.

Ignoring water quality: Hard water adds calcium and magnesium. This might mean you need less cal-mag supplement. Know your water.

Never changing solution: Even if EC looks fine, nutrient ratios drift. Regular changes prevent subtle deficiencies.

## Troubleshooting Nutrient Problems

Brown, crispy leaf tips: Nutrient burn. Solution too strong. Dilute with plain water, reduce concentration next mix.

Yellow older leaves: Usually nitrogen deficiency or pH lockout. Check pH first. If pH is fine, increase nitrogen.

Purple stems or undersides: Phosphorus deficiency or cold temperatures. Check temps. If warm enough, increase phosphorus.

Yellow between veins (interveinal chlorosis): Magnesium or iron deficiency. Often pH-related. Check pH first.

Slow growth with dark green leaves: Possibly too much nitrogen or root problems. Check roots for rot.

## UK Water Quality

UK tap water varies significantly by region. This matters because hard water already contains calcium and magnesium — two nutrients your hydroponic solution also provides.

Soft water areas (Scotland, parts of Wales, South West England): Low mineral content. Start with recommended nutrient doses and add a cal-mag supplement if plants show deficiencies like yellowing between leaf veins.

Hard water areas (most of England, particularly East Anglia and Thames Valley): High calcium and magnesium already present. You may find pH runs higher than expected even after adjusting. Reduce or eliminate cal-mag supplements. Check your local water hardness at your water company's website — anything above 200mg/l of CaCO3 is considered hard.

What this means practically: Test your tap water EC before mixing nutrients. This tells you the baseline mineral load before you add anything. In hard water areas, your starting EC might already be 0.4-0.6 before any nutrients are added. Account for this when calculating final EC targets.

## Nutrient Brands Worth Knowing

Beyond Formulex and General Hydroponics, a few other brands are worth knowing.

CANNA: Dutch manufacturer making nutrients specifically for hydroponics. CANNA Aqua is designed for recirculating systems (NFT, DWC). CANNA Coco works for coco coir growing. Clean formula, minimal residue, popular with more experienced UK growers.

Plagron: Dutch brand, widely available in UK grow shops. Reliable and consistent. Algamic (seaweed additive) is well-regarded for plant health and stress recovery during transplants.

BioBizz: Organic nutrient range. Less precise in pure water culture than synthetic nutrients but works well in coco coir. Worth knowing if you prefer organic approaches.

Where to buy: Amazon UK covers the basics. For specialist nutrients, One Stop Grow Shop and GroWell Hydroponics stock more options and staff who know UK growing conditions specifically.

## Nutrient Storage and Shelf Life

Liquid nutrients store well if kept out of direct sunlight and not subjected to freezing temperatures. Most brands last 2-3 years unopened and 12-18 months once opened. Store in a cool, dark cupboard — not a shed that freezes in winter.

Powder nutrients (some brands offer concentrated dry formulas) last longer and are cheaper to ship, but require more precise measuring. For beginners, liquids are more forgiving because small errors in measuring matter less at the volumes typically used.

Never mix concentrated nutrient solutions together before diluting. Add each part to the water separately, stirring between additions. Mixing concentrates directly can cause precipitation — visible cloudiness or sediment in your solution that represents nutrients that are now chemically unavailable to plants.

## Our Recommendations

**Best for complete beginners: Formulex* One bottle does everything. No measuring ratios, no matching A to B. Add 5ml per litre, adjust pH, done. Perfect for Kratky herbs. (Price when reviewed: ~£12 | View on Amazon)*

**Best for most growers: General Hydroponics Flora Series* Three-part system allows customisation for different crops. Extensive feeding charts available online. NASA uses it. The global standard. (Price when reviewed: ~£35 | View on Amazon)*

**Best for recirculating systems: CANNA Aqua** Specifically formulated for NFT and DWC. Very clean formula minimises buildup. Dutch quality. *(Price when reviewed: ~£30 | View on Amazon)*

Get an EC meter: Around £15-25 removes guesswork. The single most useful diagnostic tool after a pH meter.

If you haven't read it yet, our pH guide is the essential companion to this one - pH and nutrients are inseparable. And for choosing which nutrients to buy, see our best hydroponic nutrients roundup.

Take our quiz for nutrient recommendations matched to your specific crops and system type.

The nutrient knowledge you build in hydroponics applies everywhere. Understanding what nitrogen does at different growth stages, why calcium matters for fruiting crops, how EC levels affect plant uptake — these principles work whether you're in a DWC bucket, an NFT channel, or eventually an outdoor soil bed. It's not just growing knowledge. It's plant biology you'll use for years.

## Deficiency Guide

When something looks wrong, this helps narrow down the cause:

The catch: Deficiency symptoms can look almost identical to toxicity symptoms in some cases. And pH lockout looks exactly like a deficiency. That's why the diagnostic order is always pH first, then EC, then specific deficiency suspicion.

## EC/TDS Targets by Crop

EC (Electrical Conductivity) measures nutrient solution strength. Getting this right prevents both underfeeding and burning.

Always start seedlings at the lower end of the range and increase gradually.

## Mixing Nutrients: What to Do in What Order

The order matters, especially with hard water.

Recommended mixing sequence: 1. Start with fresh water in your reservoir 2. If using CalMag supplement, add first 3. Add Micro (for 3-part systems) or Part A 4. Add Grow/Bloom (Part B) 5. Stir/circulate thoroughly 6. Test and adjust pH 7. Test EC

Never mix concentrated nutrient solutions directly together before diluting — certain nutrients react and precipitate out of solution if combined at full strength.

## When to Change the Reservoir

**Recirculating systems (DWC, NFT):** Full reservoir change every 1-2 weeks. Topping up with fresh solution causes nutrient ratios to drift — certain elements deplete faster than others, and sodium and chloride from tap water accumulate.

Kratky/passive systems: Top up with plain pH-adjusted water as levels drop. Do a full change when solution is 3-4 weeks old or if plants show any deficiency symptoms despite adequate EC.

Between crops: Always do a full clean. Flush with clean water, then run a dilute hydrogen peroxide solution through the system to sanitise. Biofilm in tubing is a real source of disease problems for subsequent crops.

## Calcium and Magnesium: The UK Water Consideration

UK tap water quality varies significantly. In hard water areas (London, the Midlands), tap water contains substantial calcium and magnesium naturally. Soft water areas (Scotland, parts of Wales) have much less.

If you're in a soft water area and growing heavy feeders like tomatoes, a CalMag supplement prevents deficiencies. In hard water areas, you often get calcium and magnesium for free — sometimes more than you need.

Get your local water report from your supplier if deficiencies persist despite correct pH. The mineral content will tell you whether supplementation is warranted.

## Frequently Asked Questions

Can you use regular plant fertiliser in hydroponics?

Technically yes, but not recommended. Soil fertilisers often contain organic compounds that break down poorly in hydroponic systems and can cause biofilm, odour, and root problems. Use hydroponic-specific nutrients that dissolve cleanly.

What's the difference between grow and bloom nutrients?

Grow formulas are higher in nitrogen — for leafy, vegetative growth. Bloom formulas shift toward phosphorus and potassium — for flowering and fruiting. Herbs and lettuce primarily need grow formula. Tomatoes and peppers need bloom formula from when they start setting flowers.

My EC keeps rising even though you're not adding nutrients. Why?

Water evaporates but nutrients don't. As water level drops, nutrient concentration increases. Top up with plain pH-adjusted water (no nutrients) to bring EC back down.

How do I know which nutrients are actually being depleted?

Without lab testing, you don't know precisely. The practical answer: follow the feeding chart, do regular full reservoir changes, and let symptoms guide adjustments. More sophisticated growers use ion-specific testing, but it's unnecessary for hobby growing.

Good nutrition in hydroponics isn't about complexity — it's about consistency. Mix the same solution, test pH every time, change the reservoir on schedule, and let the plants tell you if something needs adjusting.

## Deficiency Guide

When something looks wrong, this helps narrow down the cause:

The catch: Deficiency symptoms can look almost identical to toxicity symptoms in some cases. And pH lockout looks exactly like a deficiency. That's why the diagnostic order is always pH first, then EC, then specific deficiency suspicion.

## EC/TDS Targets by Crop

EC (Electrical Conductivity) measures nutrient solution strength. Getting this right prevents both underfeeding and burning.

Always start seedlings at the lower end of the range and increase gradually.

## Mixing Nutrients: What to Do in What Order

The order matters, especially with hard water.

Recommended mixing sequence: 1. Start with fresh water in your reservoir 2. If using CalMag supplement, add first 3. Add Micro (for 3-part systems) or Part A 4. Add Grow/Bloom (Part B) 5. Stir/circulate thoroughly 6. Test and adjust pH 7. Test EC

Never mix concentrated nutrient solutions directly together before diluting — certain nutrients react and precipitate out of solution if combined at full strength.

## When to Change the Reservoir

**Recirculating systems (DWC, NFT):** Full reservoir change every 1-2 weeks. Topping up with fresh solution causes nutrient ratios to drift — certain elements deplete faster than others, and sodium and chloride from tap water accumulate.

Kratky/passive systems: Top up with plain pH-adjusted water as levels drop. Do a full change when solution is 3-4 weeks old or if plants show any deficiency symptoms despite adequate EC.

Between crops: Always do a full clean. Flush with clean water, then run a dilute hydrogen peroxide solution through the system to sanitise. Biofilm in tubing is a real source of disease problems for subsequent crops.

## Calcium and Magnesium: The UK Water Consideration

UK tap water quality varies significantly. In hard water areas (London, the Midlands), tap water contains substantial calcium and magnesium naturally. Soft water areas (Scotland, parts of Wales) have much less.

If you're in a soft water area and growing heavy feeders like tomatoes, a CalMag supplement prevents deficiencies. In hard water areas, you often get calcium and magnesium for free — sometimes more than you need.

Get your local water report from your supplier if deficiencies persist despite correct pH. The mineral content will tell you whether supplementation is warranted.

## Frequently Asked Questions

Can you use regular plant fertiliser in hydroponics?

Technically yes, but not recommended. Soil fertilisers often contain organic compounds that break down poorly in hydroponic systems and can cause biofilm, odour, and root problems. Use hydroponic-specific nutrients that dissolve cleanly.

What's the difference between grow and bloom nutrients?

Grow formulas are higher in nitrogen — for leafy, vegetative growth. Bloom formulas shift toward phosphorus and potassium — for flowering and fruiting. Herbs and lettuce primarily need grow formula. Tomatoes and peppers need bloom formula from when they start setting flowers.

EC keeps rising even though no nutrients are being added. Why?

Water evaporates but nutrients don't. As water level drops, nutrient concentration increases. Top up with plain pH-adjusted water (no nutrients) to bring EC back down.

How do I know which nutrients are actually being depleted?

Without lab testing, you don't know precisely. The practical answer: follow the feeding chart, do regular full reservoir changes, and let symptoms guide adjustments. More sophisticated growers use ion-specific testing, but it's unnecessary for hobby growing.

Good nutrition in hydroponics isn't about complexity — it's about consistency. Mix the same solution, test pH every time, change the reservoir on schedule, and let the plants tell you if something needs adjusting.

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