Water for Kratky Nutrient Solution
Water makes up almost all of a nutrient solution, so what is already in it matters. Most tap water works for Kratky growing. A quick measurement before you mix tells you whether yours needs any attention.
Start by measuring your plain water
Before adding nutrients, measure the EC (or PPM) and pH of the water itself. Water naturally carries dissolved minerals such as calcium, magnesium, sodium, bicarbonate and chloride, and these affect the strength and pH of the finished solution (Oklahoma State University Extension). A low reading leaves plenty of room for nutrients. A high reading means part of your target strength is already used up by minerals the plant may not need.
Tap water
Municipal tap water is the usual starting point and is fine for most growers. Two things to know:
- Hard water is high in calcium, magnesium and bicarbonate. Bicarbonate (alkalinity) pushes pH up, and water with alkalinity above about 75 ppm needs its pH checked more often (Oklahoma State University Extension).
- Chlorine and chloramine are added to disinfect drinking water. Chlorine leaves water that stands uncovered for a day or so. Chloramine does not. A carbon filter removes both if you are concerned.
Softened water
Salt-based water softeners swap calcium and magnesium for sodium. Sodium is not a plant nutrient and builds up as the container is drawn down. Use an unsoftened tap if you have one.
Well water
Well water varies widely. Some is soft and clean, some is very hard or high in iron or sodium. A lab test for pH, EC and alkalinity is the best first step (Oklahoma State University Extension).
Distilled and reverse osmosis water
Distilled and reverse osmosis (RO) water start close to zero EC, so the nutrient supplies everything. The trade-off is that pure water has no buffering, so pH can move more easily. Some nutrients are formulated with the assumption that tap water supplies some calcium and magnesium; check the label if you use pure water.
Rain water
Rain water is naturally soft and low in minerals, much like distilled water. Collect it from clean surfaces and containers, and measure EC and pH before using it.
Water temperature
Cool solution holds more oxygen. Oklahoma State University Extension gives 72–75 °F as an optimal solution temperature for hydroponics. Keep Kratky containers out of direct sun so the water does not overheat.
Sources
- Dunn, B. and Singh, H. Oklahoma State University Extension. Electrical Conductivity and pH Guide for Hydroponics (HLA-6722).
