For optimal growth to take place, the nutrient concentration and
pH must be consistently balanced over time to insure plants have
what they need, when they need it. In any circulating hydroponic
system, with every pass the nutrient makes past the root system, an
exchange is taking place. As a result, as time goes by, your
nutrient solution changes in concentration. Therefore, so does each
plant’s ability to uptake essential elements. The easiest way to
keep on top of your nutrient solution is to take a measurement of
PPM or TDS (Parts Per Million and Total Dissolved Solids). This
measurement is also commonly referred to as the EC or the
"Electrical Conductivity" of a solution, because that is actually
what you are measuring. There are a number of methods of
measuring PPM. My favorite is the digital PPM meter that is
submerged in the nutrient solution for a reading to be taken.
Digital PPM meters are calibrated using a solution that has a
known PPM value and you must calibrate them every so often.
But nothing beats their convenience. Frequent nutrient solution
changes will generally keep the concentration where it needs to
be. My best advice is to carefully follow the directions that come
with the nutrient you plan to use.
All the nutrients in the world will not do a plant any good if it
cannot absorb them easily. A major factor in determining a plant’s
ability to uptake nutrients is the relative acidity, or pH (the
negative log of the hydronium ion concentration) of the soil or
solution from which they feed. pH is taken by measuring a voltage
(potential) in a solution and registering it on a scale of 0-14 that
represents the concentration of hydronium ions in solution.
Generally, it is used to determine whether a solution is acidic or
basic. If your pH reading registers a 1 on the scale, this represents
a high hydronium ion concentration (an acid). Pure water is
considered neutral at a pH of 7. A 14 on the scale represents the
lowest concentration of hydronium ions (basic, alkaline).
When adjusting pH, it is best to give your fresh nutrient
mixture several hours to stabilize before attempting to adjust it.
You should also be aware that commonly available pH control
products are very powerful, and a little bit too much can sacrifice
your entire nutrient solution fast. For first timers, I would even
suggest mixing up a single gallon of nutrient solution, letting it sit
for a day, and then counting how many DROPS of pH adjustment
(up or down) it takes to get it to a range of 6.0 to 6.5. You can then
multiply your count by the volume of your reservoir as a baseline for rapid, full reservoir adjustments. Some
nutrients may become unavailable to the plant if the solution pH drifts from an optimal reading, which for most
plants is between 6.0 and 6.5. This condition is called "nutrient lockout". pH can be tested with litmus paper
and adjusted with an inexpensive pH control kit. Follow directions on product packaging.
Replacing your nutrient solution every 2 weeks is the best insurance against crop damage, as frequent
changes will provide your crop with all the nutrients it needs. Under ideal conditions, pH and PPM will drift
only slightly as the nutrient solution is used by the crop. Another great way to keep your nutrients in the
"green" is by using a larger reservoir. The extra capacity acts as a buffer and maintains pH and concentration
better than a reservoir that is "just big enough to do the job." Nutritional requirements vary throughout a plant's
life cycle. In addition, light intensity, stage of growth (vegetative or flowering), and the general size of the
plants you are growing all play a role in determining nutritional requirements. By regularly monitoring pH and
PPM, you will have the ability to make corrections to your nutrient solution before your crop suffers. There
are certain signs to look for when testing the PPM and pH of your nutrient solution. The following page
outlines these signs for you. An unusually high pH will decrease the availability of Iron, Manganese, Boron,
Copper, Zinc and Phosphorous. A pH that is too low will reduce availability of Potassium, Sulphur, Calcium,
Magnesium and Phosphorous. As a quick reference, the pH of common solutions are as follows;
Battery Acid = 1
Boric Acid = 5
Blood = 7.5
Ammonia = 11.25
Vinegar = 2.75
Milk = 6.75
Sea Water = 7.75
Bleach = 12.5
Orange juice = 4.25
Pure Water = 7.0
Borax = 9.25
Lye (caustic soda) = 13.5
znalazłem taką tabelke po polsku będzie łatwiej z tym PH 
Pozdro 
