Nutrients Requirements and Testing 5 -3

Deficiencies and Excesses
Since there is no soil to act as a buffer, your hydroponic crops will quickly respond to a nutrient deficiency or toxicity. Nutrient deficiencies are more common than excesses, with the most common deficiencies being nitrogen, iron and magnesium.

Deficiencies and excesses can be avoided by following a routine mixing procedure and schedule, daily monitoring of your nutrient solution and adequate feeding of the plants. If you have an extreme deficiency or toxicity, the plants will respond quickly and symptoms such as discoloration of foliage will occur. A minor deficiency or toxicity may not initially show symptoms but eventually will affect plant growth, vigor and/or fruiting.

Measuring Conductivity
Conductivity is a measure of the rate at which a small electric current flows
through a solution. When the concentration of nutrients is greater, the
current will flow faster. When the concentration of the nutrients is lower,
the current will flow slower.

You can measure your nutrient solution to determine how strong or weak it
is with an EC (electrical conductivity) or TDS (total dissolved solids) meter.
An EC meter usually shows the reading in either micromhs per centimeter 
(uMho/cm) or microsiemens per centimeter (uS/cm). 1.0 uMho/cm is
equivalent to 1.0 uS/cm. A TDS meter usually shows the reading in milli-
grams per liter(mg/l) or parts per million (ppm).

EC Meter

EC is generally measured at 77 F (25 C). If the temperature of the solution is raised, the EC will read higher, even though no nutrients have been  added. If the temperature drops below 77 F (25 C), the EC will decrease.
Therefore, it is important to always measure your EC at a consistent temperature of 77 F (25 C). Some EC and TDS meters compensate for varying temperatures.

Another measurement in conductivity is CF (conductivity factor) which is expressed on a scale of I -100. Pure water containing no nutrients is rated at 0 and maximum strength nutrients would rate 100.

Some general guidelines for EC levels are as follows:


 Fruiting Plants 
(such as tomatoes, cucumbers)

Leafy Plants
(such as lettuce, basil)

Initial Growth
(seedling stage)

1600 -1800 mMho/cm
1120 -1260 ppm

1400 -1600 mMho/cm
980 -1120 ppm

Average EC

2500 mMho/cm
1750 ppm

1800 mMho/cm
1260 ppm


2400 -2600 mMho/cm
1680 -1820 ppm


Low light conditions

2800 -3000 mMho/cm
2000 ppm

2000 mMho/cm
  1320 ppm

High light conditions

2200 -2400 mMho/cm
1700 ppm

1600 mMho/cm
1120 ppm

In low light conditions (winter), a hydroponic grower should increase the concentration of nutrients in solution in a hydroponic garden. In high light conditions (summer), a hydroponic grower should decrease the concentration of nutrients in solution in a hydroponic garden.

Salt Build-Ups

When a plant uses a nutrient from a chemical "salt" molecule supplied in a nutrient solution, it is actually using only one part of that molecule. The remaining part of that molecule generally stays in the hydroponic system and eventually can reach damaging levels of concentration.
This process, which often happens in traditional agriculture where heavy fertilizer concentrations are applied to soil crops, is referred to as salt-build up. By testing our nutrient solution daily. we can monitor the salt levels. If the salt levels are rising. the concentration will be higher and therefore our EC reading will be higher. In our hydroponic system, it is quite easy to resolve the problems associated with salt build-up by flushing the growing medium or replacing our nutrient solution with a fresh mix.
In the soil, once salt concentrations reach toxic levels, it is difficult to correct and often makes what was once excellent farm soil unusable. The problem is exacerbated by the salts being washed and flushed into our waterways, rivers and streams where they are also toxic to fish, birds and other wildlife.