Water has very unique density qualities. Most liquids become denser as they become cooler. Water, however, gets denser as it cools until it reaches a temperature of approximately 39ºF. As it cools below this point, it becomes lighter until it freezes (32ºF). As ice develops,water increases in volume by 11 percent. The increase in volume allows ice to float rather than sink, a characteristic that prevents ponds from freezing solid.
Being a "universal solvent," as it is sometimes called, water can dissolve more substances than any other liquid. Over 50 percent of the known chemical elements have been found in natural waters, and it is probable that traces of most others can be found in lakes, streams, estuaries, or oceans.
Dissolved Gases
Dissolved gases are those which are in a water solution. An example of gas dissolved in solution is soda water which has large quantities of dissolved carbon dioxide. The most common gases are oxygen, carbon dioxide, nitrogen, and ammonia. Concentrations are measured in parts per million (ppm) or milligrams per liter (mg/L), both units of measure are the same.
Oxygen
Dissolved oxygen (DO) is by far the most important chemical parameter.
The amount of oxygen that can be dissolved in water decreases at higher temperatures and decreases with increases in altitudes and salinites
At sea level and zero salinity, that means no nutes, 68ºF water can hold 9.2 ppm, while at 86.0F, saturation is at 7.6 ppm. In combining this relationship of decreased solubility with increasing temperatures, it can be seen why oxygen depletion are so common when higher water temperatures occur. If you live in Denver, then you will really suffer low DO at high water temps. After you add nutes,(salts) then you further decrease DO. That is why lower nutes solutions are better most of the time.
Now let's take a look at PH.
Pure water is neutral and has a pH of 7.0. Pure water consists of H20 molecules
surrounded by a relatively small number of hydrogen ions and hydroxide ions (H+ and
OH-).
Pure water is considered neutral because it has an equal number of H+ and OH-
that are freely available for chemical reaction.
Pure water has a pH of 7.0 because it contains 10-7 moles of H+ per liter and the
negative logarithm of 10-7 is 7.0.
Adding acids or bases to water changes its pH.
The pH of a sample of water is a measure of the concentration of hydrogen ions. The term pH was derived from the manner in which the hydrogen ion concentration is calculated - it is the negative logarithm of the hydrogen ion (H+) concentration. What this means to those of us who are not mathematicians is that at higher pH, there are fewer free hydrogen ions, and that a change of one pH unit reflects a tenfold change in the concentrations of the hydrogen ion. For example, there are 10 times as many hydrogen ions available at a pH of 7 than at a pH of 8.
This means a pH value below 7 is ten times more acidic than the next higher value.
For example, a pH of 4 is ten times more acidic than a pH of 5 and a hundred times (10 X 10) more acidic than a pH of 6. This holds true for pH values above 7, each of which is ten times more basic (also called alkaline) than the next lower whole value. An example would be, a pH of 10 is ten times more alkaline than a pH of 9.
The pH Scale...
The pH of water determines the solubility (amount that can be dissolved in the water) and biological availability (amount that can be utilized by aquatic life) of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.). For example, in addition to affecting how much and what form of phosphorus is most abundant in the water, pH may also determine whether aquatic life can use it. In the case of heavy metals, the degree to which they are soluble determines their toxicity. Metals tend to be more toxic at lower pH because they are more soluble.
h.
Odd as it may seem, despite being one of the most well known substances in the world, even today it's still widely studied by scientists, and there are many new properties still being discovered. One of its well known, but very interesting properties, is water's ability to dissolve into itself.
What?!?!? That's right...just as when you add common table salt (NaCl) to pure water, which quickly breaks the Na-Cl bond and dissolves it into Na+ and Cl- (called ions), when you "add pure water" (H2O) to pure water, part of it dissolves into H+ and OH-. The main difference is that, while with salt you can add several spoons into a glass and virtually all of it gets dissolved, only a very small amount of pure water gets dissolved into water.How much? Well, at room temperature, about 1 molecule in every 10 million (107) is dissolved. This means that, in a typical swimming pool full of pure water, only a few teaspoons of water would be dissolved. Now, that little number 7 up there near the 10 looks familiar, doesn't it? That's because it's exactly the number used to define "neutral pH". Note that, since each dissolved molecule of H2O results in 1 ion H+ and 1 ion OH-, these two ions are in equal amounts in pure water. The term "neutral" here means just that: the same amount of H+ and OH- ions. As mentioned above, at room temperature there's about 1 of each for every 107 molecules of water, and therefore we say that neutral water has pH=7.
And what about non-neutral water? If for any reason, the relative amount of H+ and OH- ions changes, then the water begins to drift from neutrality. If the amount of H+ ions increases, the water becomes acid, if the amount of OH- ions increases, the water becomes alkaline. For instance, suppose that the amount of H+ becomes 10 times greater than in pure water. Then there'll be about 1 H+ ion for every 1 million molecules of water (106) and therefore this water will have pH=6. Note that a change in 1 point in pH represents an increase of 10 times in the amount of H+ ions (in math this is known as a logarithmic scale). Since the amount of H+ never goes below 1 in 107 (at room temperature), the pH value for acid water will always be between 0 and 7. The value pH=0 means that there's 1 H+ ion for every molecule of water (1=100).
The same idea is used to represent increases in OH- ions. There's another scale used for this ion, called pOH, which works exactly the same: if the amount of OH- becomes 10 times greater than in pure water, then the new water will have pOH=6. For the same reasons explained above, the pOH values will always be between 0 and 7.
But using 2 scales complicates things unnecessarily, so it's more common to put both of them together in a single scale - pH. Now, instead of going only from 0 to 7, it goes from 0 to 14. The first half (0 to 7, or more accurately 7 to 0) represents increases in H+ (acid water). The second half (7 to 14) represents the increases in OH- (alkaline water). So, if you take pure water and increase the amount of OH- 10 times, the pH will raise from 7 to 8.
"Alkalinity and pH are distinctly different from each other, although their definitions and functions can be easily confused.
Alkalinity is essentially a measurement of water's ability to neutralize acids. It is a measure of the buffering capacity of a system while pH is basically the measurement of the concentration of hydrogen ions in water, in terms of acidity or alkalinity.
The alkalinity of water regarding pH issues merely refers to the basic end of a pH scale (alkaline) in contrast to the acidic end of the scale and does not reflect the buffering capacity of a system.
It is easy to believe that water with alkaline pH is likely to be high in alkalinity (buffering capacity). However, this is not necessarily true. Water with a high pH, but a low alkalinity is regarded as unstable.
Buffering capacity refers to water's ability to keep the pH stable as acids or bases are added.
pH and buffering capacity are intertwined with one another; although one might think that adding equal volumes of an acid and neutral water would result in a pH halfway in between, this rarely happens in practice.
If the water has sufficient buffering capacity, the buffering capacity can absorb and neutralize the added acid without significantly changing the pH. Conceptually, a buffer acts somewhat like a large sponge. As more acid is added, the ``sponge'' absorbs the acid without changing the pH much. The ``sponge's'' capacity is limited however; once the buffering capacity is used up, the pH changes more rapidly as acids are added.
The presence of calcium carbonate or other compounds such as magnesium carbonate contribute carbonate ions to the buffering system. Alkalinity is often related to hardness because the main source of alkalinity is usually from carbonate rocks (limestone) which are mostly CaCO3. Since hard water contains metal carbonates (mostly CaCO3) it is high in alkalinity. Conversely, unless carbonate is associated with sodium or potassium which don't contribute to hardness, soft water usually has low alkalinity and little buffering capacity. So, generally, soft water is much more susceptible to fluctuations in pH.
Buffering has both positive and negative consequences. On the plus side, the nitrogen cycle produces nitric acid (nitrate). Without buffering, your tank's pH would drop over time (a bad thing). With sufficient buffering, the pH stays stable (a good thing), is this all ringing any bell’s or what!! On the negative side, hard tap water often almost always has a large buffering capacity. If the pH of the water is too high for your plants, the buffering capacity makes it difficult to lower the pH to a more appropriate value. Attempts to change the pH of water usually fail because buffering effects are ignored.
Bicarbonate (HCO3-) and carbonate (CO32-) are the most important ions that determine alkalinity. When the carbonates accumulate in a growing medium, the growing medium solution pH reaches levels that cause plant growth inhibition, which is caused primarily by the transformation of soluble forms of Fe into insoluble forms.
Early investigations in plant nutrition demonstrated that normal plant growth can be achieved by immersing the roots of a plant in a water solution containing salts of Nitrogen (N), Phosphorous (P), Sulfur (S), Potassium (K), Calcium (Ca), and Magnesium (Mg). Hydrogen (H), Oxygen (O), and Carbon (C) are all derived from the air and water. These nine elements are defined as the macronutrients.
With further refinement in laboratory techniques, scientists established seven elements required by plants in relatively small quantities- the micronutrients or trace elements. These include Iron (Fe), Chlorine (Cl), Manganese (Mn), Boron (B), Zinc (Zn), Copper (Cu), and Molybdenum (Mo).
All plants require the same 16 elements to grow
People use the word "chemical" as if they should be cautious about these materials. The fact is, water is a chemical. Everything has chemical properties. The materials used for hydroponics are no different from that you have used traditionally in your outdoor garden just in a different original form and separated from the ground.