In hydro there's no soil to soften your mistakes. The roots sit straight in the solution, so they feel every change the moment it happens band three numbers decide whether that works for you or against you: pH, EC and water temperature. Get them right and a hydro system practically runs itself. Get them wrong and it can turn on you inside a day. Here are the target ranges and the meters you actually need to read them.
The three numbers that make or break hydro
- pH 5.5-6.5 (most growers aim 5.8-6.0) blower than soil, and it drifts fast
- EC 0.8-1.0 for young plants, building to 1.5-2.0 in peak flower
- Water temperature 18–21° - above 22B0C the oxygen drops and root rot moves in
None of these are things you can eyeball. You need a pH pen and an EC pen, and ideally a thermometer in the reservoir. That's the price of admission to hydro band it's a small one.
What pH should hydroponic ladies run at?
Hydro runs at pH 5.5-6.5, with most growers settling on 5.8-6.0. That's lower than soil's 6.0-7.0 band, because dissolved nutrients are most available to the roots right there. Drift above 6.5 and iron and manganese start to lock out; drop below 5.5 and calcium and magnesium go unavailable. The window is tighter than soil because there's no organic buffer holding it steady band hydro nutrients are slightly acidic themselves, so the solution quietly drifts more acidic over time with nothing pushing back.
That's why a reliable pH pen is non-negotiable. We stock the Bluelab pH pens and meters bthe Bluelab pH Pen is the one most of our hydro growers reach for, and it reads temperature alongside pH so you cover two of your three numbers in one tool. Keep a bottle of pH Up and pH Down beside the reservoir and it's a two-minute job each morning.
What EC should I run in hydro?
EC belectrical conductivity btells you how strong the feed is. Start low. A young plant wants barely-there feed around 0.8-1.0, and a mature plant in peak flower maybe 1.5-2.0. Build up gradually and watch the plant, because in hydro the roots taste the full strength immediately bdouble the dose carelessly and you can scorch every root tip in a week.
You can't guess EC, so a meter is essential. The Bluelab EC pens give you a clean reading in seconds, and the Bluelab Combo Meter keeps pH, EC and temperature on one device if you'd rather not carry two. One more thing while you're mixing: hydro nutrients come in A and B bottles for a reason - certain minerals turn to useless chalk if you combine them neat. Always go A into the water, stir, then B, and take your EC reading after. Browse the full pH and EC meter range to compare pens.
Why does reservoir water temperature matter so much?
Water temperature 18–21° is the number people forget, and it's the silent killer. Push past 22° and two bad things happen at once: warm water holds less dissolved oxygen, and root-rot pathogens like pythium thrive in the heat. Roots go brown and slimy within days. Keep the reservoir off the tent floor, insulated, and out of the direct path of the lights. In an Irish summer a warm tent can easily push a reservoir over the line, so a chiller is insurance rather than luxury band below 16° is too cold, because uptake stalls. Drop a thermometer in and check it with your morning pH reading.
Don't forget your starting water
Before you mix anything, check what you're starting with. Dublin tap water already sits around 0.3-0.4 EC, so you're not starting from zero bfactor that into your feed. Hard-water areas carry extra calcium that fights your pH adjustments, which is where a reverse-osmosis filter earns its keep by removing the variable entirely. And change the reservoir fully every week: topping up skews the nutrient ratios even when the EC still reads fine, so a clean refill resets the chemistry.
Pop in and we'll sort your hydro kit
If you're setting up your first hydro system and not sure which pens to start with, come in and ask bwe run this gear ourselves and we'll point you at the right meters for your setup. DIG is Ireland's largest grow shop, based in Dublin, with collection available in store and delivery across Ireland.
Want the full science behind why these three numbers matter bthe chemistry, the failure cases and the daily routine? Our friends at Grow Good Bud have the free in-depth guide.
FAQ
What pH should hydroponic ladies be?
5.5-6.5, with most growers targeting 5.8-6.0. It's lower than soil and drifts quickly, so check and adjust the reservoir daily with a reliable pH pen.
What EC should I run in hydro?
Start gentle baround 0.8-1.0 for young plants band build to roughly 1.5-2.0 in peak flower. In hydro the roots feel the full strength immediately, so increase gradually and measure with an EC meter.
Why does reservoir temperature matter so much?
Above about 22° the water holds less oxygen and root-rot pathogens thrive, so warm reservoirs cause brown, slimy roots within days. Keep it 18–21°, off the floor and insulated.
Do I need separate pH and EC meters?
You need both readings, but you don't need two devices ba combined pH/EC pen covers both, and many pH pens also read temperature. Pick whichever suits how you like to work.
Where can I buy pH and EC meters in Ireland?
DIG (Dublin Indoor Gardening) stocks Bluelab pH and EC meters along with pH adjusters and reservoir gear, with collection in Dublin and delivery across Ireland.