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Quick Summary
- Nutrient Solution: A precise mixture of water and essential minerals that feeds soil-free plants.
- pH Value: The scale measuring water acidity or alkalinity, key to preventing nutrient lockout.
- EC & PPM: Metrics used to measure dissolved salt concentration and feed strength.
- Grow Media: Inert materials like clay pebbles, coco coir or rockwool that support plant roots.
- Aeration: The process of dissolving oxygen into water using air pumps and air stones.
Starting a hydroponic garden means learning a new vocabulary. Understanding these terms isn’t about memorizing jargon, it directly impacts your daily grow decisions, from balancing a reservoir to sizing an air pump. This glossary defines the 12 essential terms every beginner needs to build a solid foundation, manage nutrient solutions and keep plants thriving.
Jump to a Key Term
Glossary of Key Terms
Nutrient Solution
A nutrient solution is a mix of water and essential minerals that plants need to grow, taking the place of soil nutrients in hydroponics. In hydroponic systems, plants get all their nutrients directly from this solution, so it’s vital to get the right balance for each plant type. Nutrient solutions typically contain elements like nitrogen, phosphorus, potassium, calcium, magnesium and micronutrients, all of which are necessary for healthy growth. Measuring the strength of this solution requires monitoring its EC and PPM nutrient concentration.
Always mix your nutrients into water one by one, never mix concentrated formulas together directly or they will chemically lock up and form an unusable white precipitate at the bottom of your bucket.
pH Level
In hydroponics, pH measures how acidic or alkaline the nutrient solution is. pH levels affect nutrient absorption, meaning if the pH is off, plants might struggle to take up vital nutrients. The ideal pH range for most hydroponic plants is between 5.5 and 6.5. Maintaining pH within this range ensures that nutrients remain available to plants, promoting growth and reducing potential problems. If your pH drifts outside this range, you will need to use pH adjusters to correct it.
Learn more: Understanding Hydroponic pH Levels and How to Manage Them
In passive systems like Kratky, pH levels tend to drift upward as plants consume water faster than nutrients, making daily checks critical during high-growth weeks.
pH Adjusters
To maintain the ideal pH range, growers use pH adjusters, which are products designed to raise or lower the pH of your nutrient solution. Common pH adjusters include products like pH Up (for increasing pH) and pH Down (for decreasing pH). Regular monitoring and adjusting are key to keeping your pH Level balanced for optimal nutrient absorption.
A mistake I made in my first year was adding pH Down directly from the bottle to a DWC reservoir without diluting it first. The sudden acid spike killed the roots of six mature lettuce plants overnight. Now, I always dilute a few drops of adjuster in a cup of water before mixing it into the reservoir to prevent shocking the plants.
Swinging pH too fast with a heavy dose of pH Down is a common beginner mistake, always adjust in small, diluted increments and recheck after 15–30 minutes of system circulation.
General Hydroponics pH Control Kit
This kit is the industry standard for adjusting reservoir pH. It contains 8 oz bottles of pH Up and Down, which last for dozens of reservoir changes, along with a liquid test indicator and vial for quick manual checks.
EC and PPM (Nutrient Concentration)
These are the two primary metrics used to measure the concentration of nutrients dissolved in your water. EC (Electrical Conductivity) measures the water’s ability to conduct electricity in milliSiemens per centimeter (mS/cm), which rises as more nutrient salts are added. PPM (Parts Per Million), also known as TDS (Total Dissolved Solids), is a conversion of that EC reading into a representation of dissolved minerals.
Actionable Baseline Numbers: As a rule of thumb, most leafy greens and herbs thrive in a low-concentration range of 0.8 to 1.5 EC (400–750 PPM), while heavy-feeding fruiting plants like tomatoes and peppers require a stronger range of 1.5 to 2.5 EC (750–1250 PPM) to support flower and fruit production.
The PPM Conversion Trap: Beginners are often confused because different meter brands convert EC to PPM using different calculations. There are two competing standards:
- 500 Scale (TDS / Hanna / Commonwealth): Converts EC by multiplying by 500. An EC of 1.0 mS/cm reads as 500 PPM.
- 700 Scale (Truncheon / 442 / Natural): Converts EC by multiplying by 700. The exact same EC of 1.0 mS/cm reads as 700 PPM.
Always check which scale your meter uses and which scale your nutrient bottle instructions reference, otherwise you risk underfeeding or severely burning your plants.
A sudden spike in EC means your water is evaporating faster than plants are consuming nutrients, which calls for topping off with plain pH-balanced water rather than adding more feed.
Grow Medium
While hydroponic plants don’t grow in soil, they do need a structure to anchor their roots in the root zone. That’s where grow mediums come in. Popular grow mediums include coco coir, perlite, vermiculite and clay pebbles, each offering different water retention and aeration properties. Your choice of grow medium can impact plant health, as it affects water availability, aeration and stability within the system.
For Deep Water Culture (DWC) systems, I’ve found clay pebbles (LECA) are the most reliable grow medium because they don’t waterlog. A common beginner mistake is starting seeds in rockwool cubes and placing them directly in DWC net cups with the water level too high, which saturates the rockwool and leads to stem rot.
If using clay pebbles, rinse them thoroughly in a bucket until the water runs completely clear; otherwise, fine red clay dust will clog your pumps and coat your root systems.
Leca Clay Pellets
Perfect for flood and drain or DWC setups, these expanded clay pebbles are porous, lightweight and hold their shape indefinitely. They provide excellent aeration and drainage for roots between watering cycles.
Hydroponic System Types
There are several types of hydroponic systems, each with unique features. The main systems include:
- NFT (Nutrient Film Technique): Nutrients flow over plant roots in a thin film, giving them direct access to water, nutrients and oxygen.
- DWC (Deep Water Culture): Plant roots are suspended in nutrient-rich water, with oxygen provided by an air pump.
- Kratky Method: A passive technique where plants grow in a nutrient-rich solution without pumps, relying on the water level gradually dropping to expose roots to oxygen.
- Drip Systems: Nutrients are dripped slowly into the grow medium, feeding plants over time.
- Ebb & Flow (Flood and Drain): A system that periodically floods the plant root zone with nutrients and then drains them back into a reservoir, drawing fresh oxygen to the roots.
- Wick Systems: A completely passive setup where a fabric wick draws nutrient solution from a reservoir up to the grow medium via capillary action.
Each system has pros and cons and your choice should come down to plant type, space and maintenance goals, our beginner’s guide to hydroponic systems walks through how to weigh NFT against DWC or Kratky for your setup. If you are interested in a dynamic flood-and-drain setup, our detailed guide to Ebb and Flow systems covers the specific pumps and fittings required.
Regardless of the system, always build your reservoir using light-proof plastic totes or paint them black; transparent containers invite algae growth that will starve roots of oxygen.
System Comparison Dashboard
Choose the right system based on your budget, space limits, and crop goals.
| System | Cost | Maint. | Oxygen Source | Best For | Primary Risk |
|---|---|---|---|---|---|
Kratky Method | $ | Very Low | Passive air gap (roots hang in air space above nutrient solution) | Herbs, lettuce, small indoor spaces, first-time growers | Silent dry-out. If the reservoir runs completely dry, roots desiccate and the plant dies quickly without warning. |
Nutrient Film Technique (NFT) | $$ | Medium | Flowing film (roots receive constant flow of shallow, aerated water) | Continuous leafy green production, growers with moderate space | Pump failure or channel clog. If the pump stops or channels get blocked by roots, crops can dry out and be lost in hours. |
Deep Water Culture (DWC) | $$ | Medium | Active aeration (roots sit in solution oxygenated by an air pump) | Fruiting plants (tomatoes, peppers), larger setups, active monitors | Root rot. Roots are submerged constantly; if oxygen drops or water temperatures exceed 75°F (24°C), fungal rot sets in fast. |
Passive air gap (roots hang in air space above nutrient solution)
Herbs, lettuce, small indoor spaces, first-time growers
Silent dry-out. If the reservoir runs completely dry, roots desiccate and the plant dies quickly without warning.
Flowing film (roots receive constant flow of shallow, aerated water)
Continuous leafy green production, growers with moderate space
Pump failure or channel clog. If the pump stops or channels get blocked by roots, crops can dry out and be lost in hours.
Active aeration (roots sit in solution oxygenated by an air pump)
Fruiting plants (tomatoes, peppers), larger setups, active monitors
Root rot. Roots are submerged constantly; if oxygen drops or water temperatures exceed 75°F (24°C), fungal rot sets in fast.
Lighting (PPFD, PAR)
In hydroponics, lighting is critical since you often grow indoors or without natural sunlight. PPFD (Photosynthetic Photon Flux Density) measures how much light reaches your plants, while PAR (Photosynthetically Active Radiation) indicates the light spectrum that plants use for growth. Adequate lighting ensures that plants can photosynthesize effectively, impacting their overall growth and yield.
Avoid the temptation to keep grow lights on 24/7; plants need a dark period to complete their respiration cycle, otherwise they will stunt and show leaf margin burn.
Root Zone
The root zone is where all the root action happens! In hydroponics, this is the area surrounding the roots that contains the nutrient solution or grow medium. Maintaining proper aeration and moisture in this zone helps promote root health, oxygen exchange and nutrient uptake. Keeping the root zone clean and free from contaminants is essential to prevent root rot and other issues.
Healthy roots should look like bright white, crisp noodles; if they start turning tan or smelling earthy, it’s an early sign that root rot pathogens are taking hold.
Reservoir
The reservoir is the tank or container that holds the nutrient solution in a hydroponic system. It can range from a simple 5-gallon bucket to a large 100-gallon reservoir. Sizing it correctly is critical; in my grows, I’ve learned that a larger reservoir is much easier to manage because the water volume buffers against rapid changes in temperature, pH and nutrient concentration.
I always size my reservoir to have at least 1.5 to 2 gallons of water capacity per mature plant to prevent the pH and water levels from fluctuating wildly during hot days.
Aeration
Aeration is the process of supplying oxygen to the root zone, typically through air stones or pumps. Since roots need oxygen to thrive, aeration is essential, especially in systems like Deep Water Culture (DWC) where roots stay submerged, our guide to air pumping in hydroponics covers how to size an air pump correctly for your reservoir. Proper aeration keeps the water moving, prevents nutrient stagnation and keeps root rot pathogens at bay.
Size the air pump to your reservoir, not just the bucket. Aim for 15 to 20 GPH (gallons of air per hour) for every gallon of water, or roughly 1 L/min for every 3.8 liters. A standard 5-gallon bucket (19 liters) needs a pump rated for at least 100 GPH, or 6 L/min, to keep the water bubbling hard and fully oxygenated.
Ensure your air pump is always placed higher than the water level in the reservoir or use a check valve, otherwise water will siphon backward into the pump when the power goes out.
VIVOSUN Air Pump Kit
A complete aeration kit with a 4-outlet commercial air pump, four air stones and non-kink tubing. Delivers up to 950 GPH (8W) with adjustable speed control to easily oxygenate multiple reservoirs or DWC buckets. Solid metal housing dampens noise and runs cool 24/7.
Venturi Pump
A Venturi pump combines air and water through a narrowing tube, creating a vacuum effect that pulls in air and disperses it as fine bubbles, effectively aerating water in hydroponic systems. In practice, you can plumb a Venturi injector directly into the outlet pipe of your main submersible water pump inside your reservoir. By adding a small bypass loop with a valve, you can divert a portion of the water flow through the Venturi to draw in outside air. This blasts a steady stream of highly aerated water back into the reservoir without requiring a separate air pump.
Plumbing a Venturi bypass to a small bypass loop off your main water pump is a great silent backup system to ensure oxygenation if your primary air pump fails.
Pest Control
Though hydroponic systems minimize soil pests, they’re not pest-proof! Common hydroponic pests include aphids, spider mites and whiteflies. Many hydroponic gardeners rely on natural pest control methods, such as beneficial insects or organic sprays, to keep pests in check without harming their plants or the environment.
In indoor setups, pests almost always enter via soil-based houseplants or on your clothes, so keep your grow room isolated and wash your hands before handling hydroponic root systems.
Next Steps
With these core terms under your belt, you’re ready to start assembling your system and mixing your first nutrient batch. Precision is key to hydroponics and having a clear handle on the terminology helps you diagnose issues early, communicate with other growers and interpret nutrient bottle instructions accurately. Experiment, keep a grow log and refer back here whenever you need a quick refresher.
Frequently Asked Questions
What is the difference between pH and EC?
pH measures the acidity or alkalinity of the water (affecting nutrient solubility), while EC (Electrical Conductivity) measures the actual concentration of nutrients dissolved in the water.
What does 'inert grow medium' mean?
An inert medium (like clay pebbles or perlite) provides physical support for the plant's roots but contains zero nutrients of its own, giving the grower complete control over feeding.
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I've been running DWC and Kratky systems for several years and write about what actually works, not textbook theory. Follow along for honest product reviews, practical guides and real grow results.
