EC and pH Monitoring Basics
Two numbers sit at the centre of nearly every feeding decision: pH determines whether nutrients are available to the roots, and EC tells you how many nutrients are in the solution. Neither number is static — they shift over time for reasons that are part of normal plant biology, not a sign that your system is failing. Understanding why they drift is the difference between chasing numbers in circles and making calm, small adjustments.
pH — the gatekeeper of nutrient availability
Most plants grown in soilless media or hydroponic systems absorb nutrients best when the root zone pH stays between about 5.5 and 6.5. Outside that range, individual elements become chemically unavailable: iron and manganese lock out on the alkaline side above neutral pH, while calcium and magnesium become harder to access in overly acidic conditions. The plant does not care what the reservoir pH reads at the start of the day — it cares about the average pH the roots experience over the full cycle between adjustments.
EC — total salt concentration, not individual elements
Electrical conductivity measures the combined concentration of all dissolved ions in the solution, expressed in millisiemens per centimetre or as parts per million depending on the meter's conversion factor. EC does not tell you which nutrients are present or in what ratios — only the total ionic strength. A rising EC in the runoff or reservoir usually means the plant is drinking more water than nutrients, concentrating the remaining solution. A falling EC suggests the opposite: the plant is pulling nutrients out faster than it is taking up water.
Why pH drifts — and why it's normal
pH drift is not a malfunction; it is a direct consequence of how roots feed. When a plant absorbs potassium, calcium, or magnesium, it releases hydrogen ions into the solution, which lowers pH. When it takes up nitrate, sulphate, or phosphate, it often releases hydroxide or bicarbonate ions, which raises pH. The direction and speed of drift depend on the nutrient formulation and the plant's current growth demands, and it can change from week to week as the plant transitions between vegetative and generative stages. A perfectly stable pH would actually be unusual in a healthy, actively feeding system.
Other causes of drift and how to manage them
Evaporation from an open reservoir concentrates the nutrient solution and raises EC without changing the nutrient ratios — top up with plain pH-adjusted water before measuring, not after. Tap water varies enormously by region: hard water with high carbonate content buffers pH upward and resists adjustment, while very soft water provides little buffering and lets pH swing rapidly. Water temperature also plays a role — warmer water speeds up chemical reactions, including the precipitation of certain nutrient compounds, and most meters are calibrated for readings at around twenty-five degrees Celsius. Check and adjust your reservoir at roughly the same time each day, record the numbers, and you will start to see the pattern rather than reacting to noise.
Key takeaway
Target pH 5.5-6.5 for most soilless grows, expect natural drift from root activity, and track trends rather than chasing a single perfect reading.