Short answer
In coco, rockwool and hydro, yes, every batch: about pH 5.5–6.2 in hydro and 5.8–6.3 in coco. In bagged soil it's good practice (pH 6.2–6.8), but the mix forgives small errors and your water's alkalinity matters more than its pH. In living soil, generally no. The ranges, soil 6.0–7.0 and soilless 5.5–6.5, are broadly agreed accepted practice. Established.
Why
pH sets how soluble each nutrient is. Above about 6.5 in soilless media, iron, manganese, zinc and boron drop out and phosphorus precipitates with calcium [1][3]. Below about 5.3, iron and manganese can reach toxic levels while calcium and magnesium fall [3].
Soilless media have little buffer. Hydro has none. Whatever pH you pour is close to what the roots get, so it must be right each time [2].
Soil buffers. Peat, compost and lime absorb small pH errors for weeks. The slow threat is alkalinity: bicarbonate in hard water acts like adding lime at every watering and pushes root-zone pH up over a grow, whatever the water's pH reads [1].
Drift within the range is normal. Aim for a band, not one perfect number.
The numbers
| Medium |
Adjust water? |
Target |
| DWC, RDWC, NFT |
Every batch |
5.5–6.2 |
| Coco, rockwool |
Every batch |
Feed 5.8–6.3, runoff 5.8–6.5 |
| Bagged soil, bottled feed |
Recommended |
6.2–6.8 |
| Living soil |
Generally no |
Root zone ~6.3–7.0 |
| Any medium, water alkalinity |
Treat if high |
Act above 100–150 mg/L as CaCO₃ |
What to do
- Calibrate your pH meter with pH 7 and pH 4 buffers.
- Hydro and coco: add nutrients, then adjust pH, every batch.
- Soil: adjust to 6.2–6.8 and check runoff monthly.
- Get a water report; acidify if alkalinity is high.
- Living soil: dechlorinate and leave pH alone.
Safety: pH down is a concentrated acid. Gloves and eye protection; add acid to water.
Common mistakes
- Skipping pH in coco "because soil doesn't need it".
- Chasing exactly 5.8 several times a day.
- pH-ing plain water before adding nutrients.
- Ignoring alkalinity.
Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Rockwool is an inert growing medium spun from melted basalt rock into fibres, sold as plugs, cubes and slabs, that holds water and air in fixed proportions.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Potting mix is a manufactured container medium, usually peat or coco with perlite, lime and starter fertiliser, designed to drain and hold air better than garden soil.Alkalinity is water's capacity to neutralise acid, mainly from dissolved bicarbonate and carbonate, reported in mg/L as CaCO3; it decides how much pH Down you need.Living soil is an organic growing medium managed to sustain an active soil food web, so microbes and invertebrates release nutrients and the soil is reused across cycles.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.General hardness (GH) is the calcium and magnesium dissolved in water, expressed as mg/L CaCO3 or German degrees (dGH); hard water supplies some Ca and Mg.DWC (deep water culture) suspends a plant's roots in an aerated nutrient solution, typically in a bucket with a net pot lid and an air stone.RDWC (recirculating deep water culture) links several aerated buckets to a central control reservoir, pumping solution through all of them to keep conditions uniform.NFT (nutrient film technique) runs a thin, continuous film of nutrient solution along sloped channels, with roots resting in the stream and exposed to air above.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.A pH meter measures solution pH with a glass electrode whose voltage changes with hydrogen ion activity; it needs regular calibration and a moist probe.
